As always, this post is a result of questions and conversations with clients.
This is a longer post because catchment is not one single thing. It is a full water system. To understand it, you have to look at the roof, gutters, tank, intake, pump, pressure system, filters, UV treatment, pH, alkalinity, and drinking water setup.
That may sound like a lot, but that is the point of this post.
Rainwater catchment is not mysterious once you break it into parts. And when those parts are designed and maintained well, catchment can produce excellent water.
On the Big Island, especially in East Hawaiʻi, many homes are not connected to public water or wells. Instead, they rely on rainwater catchment.
For buyers new to Big Island, this can sound pretty foreign at first. Most people are used to turning on the tap and not thinking much about where the water came from. So the idea of collecting household water from the roof can feel remote, off-grid, or even like a red flag.
That reaction is understandable.
But the better way to think about catchment is this: excellent water quality can be achieved with catchment, just like it can be achieved with well water or public water. The difference is that with catchment, more of the system is visible, more of it is on the property, and more of it depends on good design and regular maintenance.
With public water, most of the collection, storage, treatment, and delivery system is handled before the water reaches the house. With well water, the source and treatment system are usually private, but the water is coming from underground. With catchment, the system starts at the roof and continues all the way to the faucet.
That is the perspective I want buyers to have.
Catchment is not something to automatically avoid. It is something to understand.
A good catchment system can provide clean, clear, good-tasting water. In many homes, once the water runs through proper filtration, UV treatment, pH management, and reverse osmosis at the drinking tap, it can be excellent.
For drinking water, cooking, coffee, and ice, a properly designed catchment system with reverse osmosis can produce water that is cleaner and better tasting than what many people buy by the case at the store.
The key is understanding the whole system, not just looking at the tank in the yard.
Start with the UH Catchment Guide
For anyone who wants the comprehensive version, the University of Hawaiʻi CTAHR publication, Guidelines on Rainwater Catchment Systems for Hawaiʻi, is the main resource I recommend.
It covers the full system, including roof collection, storage, treatment, testing, maintenance, and the practical issues that come with using catchment water in Hawaiʻi. UH describes the guide as addressing water quality “from the raindrop to the faucet.”
This post is not meant to replace that guide. Think of this as the practical buyer version. These are the main parts of a catchment system I look at and talk through with clients when they are considering a property.
I have seen a lot of catchment systems on the island, and I have also built one from scratch myself. What stands out to me is that many of the better design choices are not especially complicated or expensive.
Some are simple things, such as:
- Cleaner gutter layout
- Better screening
- Easier filter access
- A proper first flush setup
- A better intake
- More thought put into the pump and pressure system
I am often surprised, even with newer construction homes, how many of these opportunities are skipped. Sometimes it may be for aesthetics. Sometimes it may be speed. Sometimes it may be cost.
But with catchment, small design choices can make a big difference in water quality, maintenance, and how the system performs over time.
Follow the Water from Roof to Faucet
The easiest way to understand catchment is to follow the water.
A typical residential catchment system may include:
- Roof surface
- Gutters and downspouts
- Gutter screens or downspout guards
- First flush diverter
- Pipe sock or inlet screen
- Storage tank
- pH and alkalinity management
- Floating intake filter
- Pump and pressure system
- Sediment and carbon filters
- UV treatment
- Reverse osmosis filter for drinking water, cooking, coffee, ice, and similar uses
The tank matters, but it is only one part of the system. The biggest mistake buyers make is thinking “catchment” means “tank.”
It is really a full water system.
When the whole chain is designed and maintained well, the system can work very well. When one part is neglected, everything downstream has to work harder.
That is the main difference with catchment. You are not just buying a water source. You are buying a water system. The quality of that system depends on how the water is collected, stored, pumped, filtered, treated, balanced, and maintained.
1. The Roof
With catchment, the roof is the first and often the most critical part of the water system.
That is one of the most important points for buyers to understand. You are not just maintaining the roof to keep the house dry. You are maintaining the roof because it is the first surface your household water touches.
Most catchment roofs in Hawaiʻi are metal, and there is a reason for that. Metal roofing is durable, sheds water well, is easier to clean than many other roof surfaces, and is generally better suited for collecting rainwater.
Composition shingles, wood shakes, and other roofing materials are usually not what you want for a catchment system.
Roof maintenance starts with the trees. You are never going to keep every leaf off a roof in East Hawaiʻi, but you can reduce the problem by trimming branches and trees that hang over the house. Less overhanging vegetation usually means:
- Fewer leaves in the gutters
- Less organic material washing toward the tank
- Fewer clogged screens
- Less opportunity for animals to access the roof
After storms, a leaf blower can be a useful maintenance tool, especially if the home has a lot of tree cover. The goal is not perfection. The goal is to reduce the amount of debris that makes its way from the roof to the gutters to the tank.
In some areas, roof maintenance can also include dealing with ash or tephra from Kīlauea activity. Fine volcanic material on the roof can wash into the catchment system if it is not managed. That is another reason roof, gutter, first flush design, and pH management matter.
Metal roofs can last a long time, sometimes 50 years or more with good maintenance, but that does not mean they can be ignored. They may need periodic cleaning, pressure washing, rust treatment, and repainting depending on age, exposure, coating, and condition.
For buyers, the point is simple: the roof is not separate from the catchment system. Roof condition, roof material, tree cover, cleaning habits, and maintenance history all affect water quality before the water ever reaches the tank.
2. Gutters and Downspouts
The gutter system is where catchment water quality really starts.
The cleaner the water is before it reaches the tank, the less the rest of the system has to deal with later. With catchment, the roof and gutter layout are not just part of the house. They are part of the water system.
This is one area where I strongly prefer a continuous overhead run from the gutter to the tank whenever possible.
A lot of newer construction sends the water underground before it reaches the tank. I understand why. It can look cleaner and more finished. But from a practical catchment standpoint, I usually prefer to see the water stay above ground and travel directly from the gutter to the tank in a visible, sloped overhead run.
The reason is simple. When the water goes underground and then has to come back up into the tank, there is almost always a section of pipe that holds water between rain events. That means standing water sits in the line instead of draining out fully. Over time, that can create more opportunity for sediment, organic material, and stagnant water to collect in the system.
With a continuous overhead run, the water can usually travel downhill to the tank and drain out much more completely after the rain stops. That is a basic but important advantage.
This approach also makes the system easier to clean, easier to flush out, and easier to service. It is generally easier to install a first flush diverter in a practical location, and easier to understand what is happening in the line if something needs attention.
So for me, this is not mainly about whether the piping looks cleaner or whether you can see it. It is a different design approach for a basic practical reason: I would rather see a line that drains than a line that holds water.
That does not mean every underground run is automatically bad. Some work fine. But if I were designing a catchment system from scratch, I would usually prefer to keep the water in a visible overhead run from the gutter to the tank rather than sending it underground and back up again.
Gutter maintenance is part of the deal. After heavy storms, wind events, or ash events, gutters may need to be cleaned with a leaf blower, hose, gutter scoop, or sometimes by hand. The more trees around the house, the more often this needs to happen.
Clogged gutters do not just affect drainage. They affect the quality of the water going into the system.
3. Gutter Screens, Leaf Guards, and Downspout Guards
Before water ever reaches the tank, the system should try to keep out as much debris as possible.
There are different ways to do this. Some homes use full gutter guards that cover the entire length of the gutter. These get mixed reviews. In theory, they keep leaves out of the gutter. In practice, they can get covered with leaves and debris, especially in heavily treed areas. When that happens, water may run over the top instead of flowing cleanly into the gutter.
That does not mean full gutter guards are always bad, but they need to be matched to the property and maintained. In East Hawaiʻi, with heavy rain, trees, and fast-growing vegetation, anything that sits on top of the gutter can become its own maintenance issue.
My preference is usually simpler: inexpensive downspout guards or screens at the gutter outlet. They are easy to see, easy to remove, easy to clean, and easy to replace. They do not solve every problem, but they can keep larger debris from entering the downspout and moving toward the tank.
Maintenance here is simple but important. Downspout guards need to be checked often, especially after storms. If they are packed with leaves, they can block water from getting to the tank.
Full-length gutter guards need to be checked too, because a guard covered in wet leaves can cause the water to sheet over the gutter instead of entering it.
The goal is not to create a perfect system that never needs attention. The goal is to keep the biggest debris out early and make the parts easy enough to clean that they actually get maintained.
This is another example where simple and serviceable may be better than something that looks more finished but is harder to manage over time.
4. First Flush Diverter
The first rain after a dry period washes the roof. That first runoff can carry dust, pollen, leaves, bird droppings, ash, tephra, and other debris.
A first flush diverter sends the dirtiest initial water away from the tank before cleaner water continues into storage.
This is a good example of a relatively simple feature that can make a meaningful difference. I am surprised how often I see systems without one, even on newer homes.
A first flush system also needs to be designed so it can be drained, cleaned, or serviced. Like the rest of the system, it only helps if it is maintained.
Maintenance matters here too. A first flush diverter that never gets drained or cleaned can become its own dirty water chamber. The diverter should be accessible, easy to drain, and easy to inspect.
After long dry periods, big storms, or ash events, it is worth paying extra attention to this part of the system.
5. Pipe Sock or Tank Inlet Screen
After the gutters and first flush, the next step is usually some type of screening before water enters the tank.
A pipe sock or inlet screen catches additional debris before water enters the tank.
This is simple, inexpensive, and important. It also needs to be checked and cleaned. A clogged sock or screen can create overflow or reduce how much water actually reaches the tank.
Like many parts of a catchment system, it only works if someone can access it and maintain it.
Maintenance here should be routine. If the inlet screen or pipe sock is doing its job, it will catch debris. That means it will also need to be cleaned. If it is ignored, water may bypass the screen, overflow, or fail to reach the tank efficiently.
6. Tank Type and Volume
Once the water reaches the tank, storage becomes the next big question.
Tank size matters, but there is not one right answer for every property.
On the Big Island, you will see catchment tanks as small as about 2,500 gallons, and you will also see systems with 10,000, 15,000, 20,000 gallons or more. The right size depends on:
- The home
- The number of people living there
- The amount of roof area collecting water
- The local rainfall pattern
- Landscaping needs
- How much cushion the owner wants during drier stretches
This is one reason local knowledge matters. Some parts of East Hawaiʻi receive so much rain that a smaller tank may work fine for a modest home with normal household use. Other areas may still be wet compared with many mainland locations, but they can have longer dry periods or more variation, so extra storage becomes more important.
Volume is not only about drinking water or showering. Buyers should also think about leaks, guests, laundry, landscaping, pressure washing, and emergencies. A small leak that goes unnoticed can drain a smaller tank faster than people expect. A larger tank gives you more time to catch a problem and more margin when conditions are not ideal.
Insurance can also come into play. Some insurance companies may have minimum catchment tank requirements, not because they are focused on your drinking water capacity, but because they are thinking about fire protection and emergency water availability.
For example, my own insurer, State Farm, has required 10,000 gallons for my property. That does not mean every company or every policy will have the same requirement, but it is something buyers should ask about early, especially when comparing homes with smaller tanks.
Common catchment tanks in Hawaiʻi include:
- Metal tanks with liners
- Plastic or poly tanks
- Concrete tanks
- Older wood or fiberglass systems
On many older homes, you will also hear the term “Doughboy” tank. These are basically above-ground swimming pool-style tanks that have been adapted for catchment use with a food-grade liner. They are common enough that buyers will run into them, especially on older properties.
Most new construction homes I see use corrugated galvanized steel tanks with liners. These can work well, but the same basic questions still apply:
- What is the tank size?
- What condition is the liner in?
- Is the cover secure?
- Is the tank protected from debris, sunlight, animals, and overflow issues?
The tank type matters, but the condition and setup matter just as much. A newer tank that is poorly covered, poorly plumbed, or hard to maintain may not be better than an older tank that has been properly cared for.
Tank maintenance includes checking the cover, liner, overflow, fittings, and general condition. The cover should be secure. The liner should be in good shape. Overflow should be directed where it will not damage the house, foundation, driveway, or yard. Vegetation around the tank should be managed so the area stays accessible.
When looking at a home, I want to know:
- How many gallons does the tank hold?
- What type of tank is it?
- Is the tank size appropriate for the home, location, and household use?
- Does the tank size meet any insurance requirement for the property?
- Is the tank covered?
- Is the liner in good condition?
- Is the cover secure enough to keep out animals, leaves, sunlight, and debris?
- Where does the overflow go?
- Is there reasonable access for inspection and maintenance?
- Is the storage appropriate for the house, household size, and location?
On the east side of the Big Island, rainfall is usually not the issue in the same way it can be in drier areas. But that does not mean tank size is irrelevant. A larger tank gives you more flexibility, more room for changing weather patterns, and more cushion if something goes wrong.
7. pH, Alkalinity, and Acidic Catchment Water
Another issue buyers should understand is pH and alkalinity.
Rainwater is naturally soft and often acidic. On the Big Island, this can be more of an issue because volcanic emissions can contribute to acid rain, and ash or volcanic material on the roof can add another layer of concern for catchment systems.
USGS notes that sulfuric acid in vog can create acid rain, which can leach lead and copper from roofing and plumbing materials. UH also notes that acid rain in catchment systems can leach metals from roofs, tanks, coatings, pipes, and fixtures.
This is not just about taste. Acidic water can be corrosive. In a home with copper plumbing, low-pH water can contribute to copper pipe degradation and blue-green staining at sinks and tubs. It can also increase the risk of lead or copper showing up in the water if the system has older materials, solder, flashings, or other metal components.
For buyers, the practical issue is this: water can look clear and still be too acidic. That is why pH testing matters.
UH describes pH as the measure of whether water is acidic or basic, with 7 being neutral, below 7 acidic, and above 7 basic. UH also notes that most drinking water is in the pH 6.5 to 8.5 range.
There are a few ways homeowners deal with acidic catchment water.
Treating the Tank
Some homeowners treat the water in the tank by adding baking soda or soda ash to raise pH and alkalinity.
UH has recommended dissolving baking soda in water and adding it to the tank during vog-related acid rain conditions to help raise pH and reduce copper and lead leaching. This kind of approach can be simple and inexpensive, but it needs to be done thoughtfully, with testing, because every tank and water condition is different.
Whole-House pH Treatment
Another approach is a whole-house pH neutralizing filter or alkaline filter installed after the tank and before the water moves through the rest of the treatment system.
These systems may use neutralizing media to raise pH as the water passes through. The advantage is that the water can be treated before it goes through the home’s plumbing, which may help protect pipes, fixtures, and equipment.
RO Remineralization
A third place people address alkalinity is at the drinking water stage, especially with reverse osmosis.
RO systems often remove minerals, so many systems add a remineralization cartridge after the RO membrane. That can improve taste and add some minerals back into the drinking water.
But this only treats the water at that drinking tap. It does not protect the whole plumbing system from acidic water.
So there are really two different questions:
- Do you need to adjust pH for the whole house to protect the plumbing and system?
- Do you want remineralization at the RO tap to improve drinking water taste?
Those are related, but they are not the same thing.
For buyers, I would want to know whether the catchment water has been tested for pH, lead, and copper, especially in areas affected by vog, ash, or older construction materials.
The Hawaiʻi Department of Health currently describes a lead and copper testing program for individual homes served by rainwater catchment systems.
Maintenance here means testing periodically and adjusting the system based on actual results. If the pH is low, the owner may need to treat the tank, maintain a neutralizing filter, replace alkaline media, or adjust the drinking water system.
Like the rest of catchment, it is manageable, but it should not be ignored.
8. Floating Intake Filter
Once water is stored in the tank, the next question is how water is pulled from the tank and sent toward the house.
A floating intake draws water from below the surface but above the sediment at the bottom of the tank.
That can help the system pull cleaner water into the house compared with drawing directly from the bottom where sediment collects.
This is another design choice that may not be obvious to a buyer at first glance, but it can matter. Where the system draws water from inside the tank affects what gets sent toward the pump and filters.
Maintenance here is mostly about inspection. A floating intake should actually float, stay screened, and remain connected. If the intake is damaged, clogged, disconnected, or sitting at the bottom of the tank, it is not doing what it is supposed to do.
9. Pump, Pressure Tank, and On-Demand Pumps
The tank stores the water. The pump makes the house feel normal.
Many catchment homes use a traditional pump and pressure tank. The pump moves water from the tank into the house. The pressure tank helps maintain steady pressure and reduces how often the pump cycles on and off.
Some systems use a shallow well pump setup with a pressure tank. Others use booster pump configurations depending on the layout, distance, elevation, and household demand.
This is another part of the system that affects daily life. If the pump and pressure system are sized and installed well, the home can feel like any other home when you turn on the faucet or take a shower. If the pressure tank is too small or the pump is short cycling, you may notice pressure changes, noise, or extra wear on the equipment.
A larger pressure tank can help smooth out water delivery and reduce pump wear.
I am also seeing more modern on-demand or constant-pressure pump systems in newer builds. These systems can reduce or eliminate the need for a separate traditional pressure tank. That means one less large component to install, maintain, and eventually replace.
The tradeoff is cost and complexity. These systems are often more expensive than a basic pump and pressure tank setup, and if something goes wrong, service may be more specialized.
For a buyer, the question is not whether one system is automatically better. The question is whether the pump system is appropriate for the house, easy to service, protected from weather, and supported by someone locally who knows how to work on it.
Pump maintenance means paying attention to pressure, leaks, noise, cycling, and protection from weather. If the pump is turning on and off constantly, that can shorten its life. If the equipment is exposed to rain, mud, or vegetation, it may not last as long.
A good setup should be accessible, protected, and easy to service.
When evaluating a system, I want to know:
- Does the home use a traditional pump and pressure tank, or a modern on-demand/constant-pressure pump?
- Does the pump turn on and off normally?
- Is the pressure steady at fixtures?
- If there is a pressure tank, is it properly sized?
- If it is an on-demand pump, is it properly sized and serviceable locally?
- Is there a pressure gauge or readable control panel?
- Are there leaks at the pump, fittings, or filter housings?
- Is the equipment protected from weather?
- Is there a bypass or shutoff setup that makes service easier?
A good pump setup is easy to forget about because it just works. A bad setup becomes part of daily life very quickly.
10. Whole-House Sediment, Carbon, and pH Filters
After the water is pulled from the tank and pressurized, it should usually pass through whole-house filtration before it reaches the plumbing fixtures.
Many systems use two-stage or three-stage whole-house filters. The idea is simple: each stage removes smaller particles or handles a different part of the job.
A common setup may start with a larger sediment filter, such as 20 microns or 10 microns, followed by a smaller sediment filter, such as 5 microns or 1 micron. Some systems then add a carbon filter to help with taste, odor, and some organic material.
The exact setup can vary, but the sequence matters. You usually do not want the smallest, finest filter doing all the work first. A larger sediment filter can catch the bigger material before the water moves to a finer filter. That helps the finer filter last longer and keeps the system flowing better.
Carbon filters are also common, but they are not a magic fix by themselves. They are one stage in a larger system. They can help improve taste and odor, but they still need to be replaced and should be used in the right order with the other filters.
Whole-house filtration is also where pH treatment may fit into the system. If the catchment water is acidic, some homes use a neutralizing or alkaline filter before the water moves through the rest of the plumbing.
That is different from remineralization at an RO faucet. A whole-house pH treatment setup is about protecting the plumbing and system. RO remineralization is mostly about the taste and quality of drinking water at one tap.
Filter placement matters too. Filters should be accessible enough that the homeowner can actually service them. If changing filters is difficult, messy, or inconvenient, it is less likely to happen on schedule.
This is one place where I often see missed opportunities. A better filter setup does not always require a massive investment. Sometimes it is about using the right sequence, leaving enough room to service the filters, and installing the system where it can be maintained without a hassle.
Filter maintenance is not optional. Sediment filters, carbon filters, and pH neutralizing media need to be serviced. How often depends on the system, water quality, usage, and manufacturer recommendations.
If the filters are dirty or clogged, water pressure can drop and the UV system may not work as well. A filter setup that is easy to access is more likely to be maintained properly.
11. UV Treatment
After sediment, carbon, and any needed pH treatment, many catchment systems use UV treatment.
This is where the water passes through a chamber with an ultraviolet bulb. The water flows past the bulb, and the UV light is used to neutralize bacteria and other microorganisms before the water continues into the house.
People sometimes describe this as “cooking” the bacteria, but it is not cooking in the heat sense. The water is not being boiled. The UV light damages microorganisms so they cannot reproduce and continue causing problems.
That is why the water needs to be clear before it reaches the UV unit. If the water is cloudy or full of particles, bacteria can hide behind sediment and the UV light may not reach everything effectively.
So the sequence matters. Sediment filtration before UV is not just a nice extra. It helps the UV system do its job.
UV systems also need regular maintenance. The bulb does not last forever, and it may still glow even after it is no longer effective enough for proper treatment. Many UV bulbs are replaced about once a year, depending on the system and manufacturer’s recommendation.
These bulbs are not always cheap, so buyers should understand that UV treatment is an ongoing maintenance item, not a one-time installation.
Many systems include a countdown timer, warning light, or alarm to remind the owner when the bulb is due for replacement. That is helpful, but only if the owner pays attention to it.
The sleeve around the bulb may also need to be cleaned, especially if minerals or film build up over time. A dirty sleeve can reduce how much UV light reaches the water.
A UV system that is installed but ignored should not give buyers false confidence. It needs to be working, properly sequenced after filtration, and maintained on schedule.
12. Reverse Osmosis for Drinking Water
The final stage for many homes is reverse osmosis at the kitchen sink, refrigerator line, or both.
For drinking water, cooking, coffee, tea, and ice, many homeowners add a reverse osmosis filter. This is the final polish.
Reverse osmosis works by pushing water through a very fine membrane that removes many dissolved solids and other contaminants. In a catchment system, that can be a very good final step after the water has already gone through:
- Roof collection
- Tank storage
- Sediment filtration
- Carbon filtration
- pH management, if needed
- UV treatment
With a good catchment system, proper filters, UV, and RO at the drinking tap, the water can be excellent. This is where catchment can surprise people. The same buyer who was nervous about roof-collected water may end up with drinking water that tastes better than what they had on public water or what they can buy in a store.
One thing to understand about RO systems is that they can remove some of the minerals that affect taste and mouthfeel. People sometimes call these the “good minerals,” such as calcium and magnesium. That does not mean RO water is bad, but it can taste a little flat to some people because so much has been removed.
For that reason, many RO systems include a remineralization filter as a final stage. After the water passes through the RO membrane, the remineralization filter adds a small amount of minerals back into the water. This can improve taste, add some alkalinity, and make the water feel less stripped down.
A remineralization filter at the RO system can improve taste and add some minerals back into the drinking water, but it does not fix acidic water for the whole house.
If low pH is affecting copper pipes, fixtures, or the broader plumbing system, that should be addressed earlier in the system, either at the tank or with a whole-house pH or alkalinity treatment setup.
So when I look at an RO setup, I want to know whether it is a basic RO system or an RO system with remineralization. Both can work, but buyers should understand the difference.
RO systems also need maintenance. Pre-filters, carbon filters, RO membranes, and remineralization cartridges all need to be replaced on schedule. The storage tank and lines should also be checked if taste, flow, or pressure changes.
This is not complicated, but it does need to be done.
For drinking water, cooking, coffee, and ice, a properly maintained RO system with remineralization can be a strong final step in a catchment system. It is one more example of how catchment water, when handled correctly, can be very high quality.
Maintenance Is Not Optional
Catchment systems are not difficult, but they are not “set it and forget it” either.
That is probably the most practical difference between catchment and public water. With public water, most homeowners do not think about collection, storage, treatment, or pressure until something goes wrong. With catchment, the homeowner needs to pay attention before something goes wrong.
Basic maintenance includes:
- Trimming branches and trees that hang over the roof
- Cleaning or blowing debris off the roof after storms
- Cleaning gutters after storms, wind, heavy leaf drop, or ash events
- Keeping the roof reasonably clean
- Pressure washing, treating rust, or repainting the roof when needed
- Checking gutter screens, downspout guards, and first flush devices
- Cleaning pipe socks and inlet screens
- Checking the tank cover and liner
- Watching for overflow, leaks, or low water levels
- Testing pH, lead, copper, and basic water quality periodically
- Treating the tank or maintaining a neutralizing filter if pH is low
- Checking the floating intake if accessible
- Watching pump pressure, pump cycling, and leaks
- Replacing sediment and carbon filters
- Servicing pH neutralizing media if installed
- Servicing or replacing the UV bulb as recommended
- Cleaning the UV sleeve when needed
- Maintaining the RO system for drinking water
- Replacing remineralization cartridges if installed
- Watching for unusual taste, odor, staining, or pressure changes
- Testing the water periodically
Private residential catchment systems are generally the homeowner’s responsibility. That means the owner needs to understand the system and take the maintenance seriously.
The upside is that the system is also within the homeowner’s control. You can improve filtration. You can add UV. You can add reverse osmosis. You can upgrade the pump or pressure system. You can treat pH and alkalinity. You can clean up the roof and gutter collection system.
With catchment, the quality of the system is not fixed. It can often be improved.
That is one of the reasons I like educating buyers about it. Once they understand the parts, catchment becomes less mysterious and more manageable.
Evaluating A Catchment System
If you are buying a home with catchment, upgrading your catchment system or just want to understand more, here are all the things you should consider:
Roof, Trees, and Gutters
- What type of roof does the home have?
- What is the roof condition?
- Are trees or branches hanging over the roof?
- Does the roof show rust, heavy debris, moss, staining, ash, or signs it may need cleaning or repainting?
- Are the gutters clean and properly sloped?
- Are there full gutter guards, downspout guards, or screens?
- Are those guards easy to access and clean?
- Does the water travel in a continuous overhead run from the gutter to the tank, or does it go underground first?
- If it goes underground, does the line hold standing water between rain events?
- Is there a practical place for a first flush diverter and line cleanout?
- Is there a pipe sock or inlet screen?
Tank and Storage
- What is the tank size?
- What type of tank is it?
- How old is the tank and liner?
- Is the tank size appropriate for the home and location?
- Does the tank size meet any insurance requirement?
- Is the tank covered and screened?
- Where does the overflow go?
pH, Testing, and Water Quality
- Has the catchment water been tested for pH?
- Has it been tested for lead and copper?
- Is there blue-green staining at sinks or tubs that could suggest copper leaching?
- Is pH being treated at the tank, with a whole-house neutralizing filter, or only at the RO drinking water tap?
- If there is a neutralizing or alkaline filter, when was the media last serviced or replaced?
- Has the water been tested recently?
Pump, Pressure, Filters, UV, and RO
- Is there a floating intake?
- Does the home use a traditional pump and pressure tank, or an on-demand/constant-pressure pump?
- Is the pump protected and working properly?
- Is the pressure steady at fixtures?
- What filters are installed?
- Are the filters two-stage, three-stage, or something else?
- When were the filters last changed?
- Is there UV treatment?
- When was the UV bulb last replaced?
- Does the UV unit have a countdown timer, warning light, or alarm?
- Is there reverse osmosis for drinking water?
- Does the RO system include remineralization?
- Are there receipts, service records, or installation information?
None of these questions are meant to scare a buyer away. They are meant to help the buyer understand what they are buying.
The goal is not to make catchment sound complicated. The goal is to make it understandable.
My Take
I do not see rainwater catchment as a negative.
On this side of the island, it is a normal part of life for many properties. In the right setup, it can provide excellent water.
But I do see a big difference between a basic tank with minimal filtration and a well-thought-out system with good collection, storage, pH management, pumping, filtration, UV treatment, RO drinking water, and a realistic maintenance routine.
That is the perspective I want buyers to have. Catchment is not second-class water. It is an owner-managed water system.
With public water, you usually inherit the public system and then deal with what reaches the house. With well water, you need to understand the well, pump, pressure system, and treatment. With catchment, you need to understand the roof, gutters, tank, pH, pump, filters, UV, RO, and maintenance.
Different systems. Same basic goal: clean, reliable water.
The reality is that catchment is work. Not impossible work, and not necessarily expensive work, but regular homeowner work. You have to pay attention to the roof, trees, gutters, screens, tank, pH, pump, filters, UV system, and drinking water setup.
That is part of the tradeoff.
For many people, that tradeoff is worth it. Catchment is one of the systems that makes it possible to live affordably in some of the most beautiful parts of the Big Island, including areas that do not have public water. You take on more responsibility, but you also get to live in places where public infrastructure may never reach.
Once you understand catchment, it becomes much less mysterious. And in the right setup, it can be one of the better parts of the property.