Buying a Home with Catchment Water on the Big Island: What Every Buyer Should Know
If you're considering purchasing a home on the Hamakua Coast, Hilo, Hawaiian Paradise Park, or other rural areas of the Big Island, one of the most important things to understand is the property's water source. While many homes are connected to the County water system, thousands of homes throughout East Hawaii rely on rainwater catchment systems.
I've personally lived with a catchment system for five years while living off-grid in Hawaiian Paradise Park (HPP) in the Puna District, where catchment water is the norm. Like many buyers moving to Hawaii from the mainland, I had a lot to learn at first. After maintaining my own system and helping clients purchase homes with catchment, I've found that a properly maintained system can provide an excellent, dependable source of water.
Whether you're buying your first catchment home or simply want to know what to inspect, here are the most important things to look for.
Does the Property Have County Water or Catchment?
Before purchasing a home, always determine whether the property is connected to the County water system or relies on rainwater catchment.
Throughout much of the Hamakua Coast, Puna, and other rural parts of the island, many properties are too far from County water infrastructure and therefore rely entirely on catchment systems.
Neither option is inherently better—it simply comes down to understanding the maintenance involved. If you're purchasing a catchment property, make sure you're comfortable caring for the system or hiring someone to maintain it.
How a Catchment Water System Works
Rainwater catchment systems are actually quite simple.
Rain falls onto the home's roof, flows into the gutters, travels through downspouts, and is directed into the catchment tank where it is stored.
When you turn on a faucet, a water pump pulls water from the tank and sends it through the home's filtration system before it reaches your plumbing fixtures. Most catchment systems also include a pressure tank, which stores pressurized water so the pump doesn't have to turn on every time you open a faucet. This reduces wear on the pump and helps maintain consistent water pressure throughout the home. Some newer variable-speed pump systems no longer require a separate pressure tank, so don't be surprised if you encounter either type of setup while touring homes.
Because your roof is the surface collecting your drinking water, it should be made from materials appropriate for potable rainwater collection and be kept clean. The gutters should also be maintained so leaves and debris don't continually enter the system.
Common Types of Catchment Tanks
There are several different styles of catchment tanks you'll encounter on the Big Island.
Corrugated Steel Tanks
These are by far the most common today.
A corrugated galvanized steel shell surrounds a food-grade plastic liner, typically made from polyethylene or polypropylene. The liner is what actually holds the water and prevents it from contacting the metal tank.
Polyethylene (Plastic) Tanks
One-piece polyethylene tanks are becoming increasingly popular.
Because they're completely enclosed, they reduce the opportunity for insects, frogs, rodents, and other pests to enter the water supply. They're also very durable and require less maintenance than some older tank styles.
Older Concrete and Fiberglass Tanks
You'll occasionally find older homes with concrete or fiberglass catchment tanks. Many of these systems continue to function well, but they should be inspected carefully due to their age.
Inspect Both the Tank and the Liner
When inspecting a catchment system, don't just look at the outside of the tank.
Take a close look at the liner as well.
The liner should be free from:
Tears
Holes
Brittleness
Excessive staining
Signs of deterioration
A damaged liner can compromise water quality and eventually require replacement.
Also inspect the tank itself for:
Rust (if applicable)
Structural damage
Properly sealed lid
Screened overflow
Evidence of algae or excessive sediment
Understanding the Filter System
A properly maintained filtration system is essential.
20-Micron Sediment Filter
The first stage is typically a 20-micron sediment filter.
This removes larger debris such as:
Dirt
Sand
Leaves
Small insects
Sediment
Replacing this filter regularly protects the finer filters downstream.
0.5-Micron Carbon Filter
Next comes the 0.5-micron carbon filter.
This filter helps:
Improve taste and odor
Remove chlorine or bleach used to disinfect the tank
Capture very fine particles
Replacing this filter on schedule is one of the most important maintenance items in the entire system.
Make Sure the UV Sterilizer Matches the Pump
The UV sterilizer is one of the most overlooked components of a catchment system.
Its job is to expose water to ultraviolet light long enough to inactivate bacteria and other microorganisms before the water enters your home.
One mistake I occasionally see is homeowners replacing the UV unit with one that isn't properly matched to the home's water pump.
If water flows through the UV chamber faster than the unit is designed to handle, the exposure time may be reduced, making the sterilization process less effective.
Whenever replacing a UV sterilizer, make sure its rated flow capacity matches the output of your water pump.
Catchment Tank Maintenance
One of the questions I hear most from buyers is, "How much maintenance does a catchment system require?" The good news is that a well-maintained system is relatively straightforward, especially once you understand the routine.
Typical maintenance includes:
Periodically cleaning the roof and gutters so leaves, dirt, and other debris don't wash into the tank.
Inspecting the tank lid, overflow screens, and vents to make sure pests cannot enter the system.
Monitoring the condition of the liner and checking for any signs of leaks or excessive wear.
Replacing the sediment, carbon, and UV filters according to the manufacturer's recommended schedule.
Replacing the UV bulb at the recommended interval, even if it still illuminates, since its germicidal effectiveness diminishes over time.
Occasionally disinfecting the catchment tank with an appropriate amount of chlorine or bleach when needed, following accepted water treatment guidelines.
Cleaning the inside of the catchment tank periodically to remove sediment that naturally accumulates over time.
Many homeowners also keep an eye on the water level during extended dry periods. Fortunately, water delivery services are available throughout much of the Big Island if the tank ever needs to be replenished.
Like any major system in a home, regular maintenance goes a long way. A catchment system that is inspected and serviced on a routine basis can provide reliable, high-quality water for many years.
Our Drinking Water Setup
Although the home's filtration system provided treated water throughout the house, for many years my wife and I chose to use a Berkey gravity water filter for our drinking water.
It provided one additional level of filtration before the water reached our glass and gave us extra peace of mind.
Many homeowners choose a similar setup, while others install an under-sink drinking water filtration system. Either approach can provide an additional layer of treatment for the water you drink every day.
Seeing Particles Even After Replacing the Filters?
Sometimes homeowners install brand-new filters and still notice particles coming from the faucets.
Often, the issue isn't the catchment tank—it's the plumbing inside the home.
One effective way to sanitize the plumbing is by disinfecting the water lines themselves.
Rather than heavily chlorinating the entire catchment tank, I prefer a more targeted approach.
Remove the filter from the filter housing and place a concentrated bleach solution inside the empty housing. Then run the faucet that's farthest from the filtration system until you begin to smell bleach. Once you know the disinfectant has reached the end of the plumbing system, allow it to remain in the pipes for the recommended contact time before thoroughly flushing the system with fresh water. Install new filters afterward before placing the system back into service.
If you're unfamiliar with this procedure, consult the filter manufacturer or a qualified water treatment professional before performing the work.
What Happens if You Run Out of Water?
One question I hear from mainland buyers is:
"What happens if the tank runs dry?"
Fortunately, there are companies throughout the Big Island that deliver potable water.
Pricing varies depending on your location, accessibility, and current fuel costs, but a full truckload is often surprisingly affordable compared to what many buyers expect.
In most years, many homeowners never need a delivery at all. During particularly dry summers, however, some homeowners—especially in lower elevation or drier areas—may choose to have water delivered to top off their tanks until the rainy season returns.
Questions Every Buyer Should Ask
Whenever I'm helping clients purchase a home with catchment, we evaluate questions such as:
How old is the catchment tank?
What condition is the liner in?
When were the filters last changed?
How old is the UV bulb?
Does the UV sterilizer match the pump's flow rate?
Has the tank been cleaned recently?
Are replacement filters readily available?
Is County water available now or planned for the future?
These questions can provide valuable insight into both the condition of the system and the maintenance you can expect after moving in.
A Note from Personal Experience: Installing a Catchment Tank
Having lived off-grid in Hawaiian Paradise Park, I not only maintained a catchment system—I also built and installed my own catchment tank. It gave me a real appreciation for how important proper installation is to the long-term performance of the system.
For liner-style catchment tanks, one of the most critical parts of the installation is preparing the foundation. Many systems are installed on a concrete slab or concrete ring with a carefully prepared base of compacted rock or gravel topped with a layer of fine sand. The goal is to create a level, stable surface that fully supports the liner.
During installation, it's important to inspect the sand carefully. Even small rocks protruding through the sand can eventually wear against the liner and create a leak. When I installed mine, I spent time on my hands and knees removing any sharp rocks and adding additional sand where needed to create a smooth surface.
Another important step happens while the tank is being filled for the first time. Someone should be inside the liner, following the manufacturer's safety and installation recommendations, smoothing out folds and creases as the water level rises. Large creases can create stress points that may shorten the life of the liner over time.
Most homeowners will never have to install a catchment tank themselves, but understanding how these systems are constructed can help you recognize the value of a well-installed tank and appreciate why the condition of both the liner and its foundation are important during a home inspection.
Final Thoughts
Rainwater catchment systems are simply a way of life throughout many parts of the Big Island. Like a septic system or private well on the mainland, they require periodic maintenance—but when properly cared for, they can provide a dependable, high-quality source of water for many years.
If you're considering purchasing a home on the Hamakua Coast, Waimea, Hilo, Puna, or anywhere else on the Big Island, I'd be happy to help you evaluate not only the home itself, but also the water system, septic system, and other unique aspects of island living so you can make an informed decision.
Peter Prentiss
The Agency Team Hawaii | eXp Realty
Helping buyers and sellers navigate real estate on the Hamakua Coast, Waimea, Hilo, North Hawaii, and throughout the Big Island.
