Many homes in rural Hawaii do not have access to county water or sewer. These households are responsible for providing their own water and sewer. Porous volcanic rock doesn't lend itself to digging wells so most people use rain catchment water. Simply speaking, the water that comes off the roof is captured and stored. It is treated before being used. Displayed above is a picture of our roughly 10,000 gallon water catchment tank. Based on our annual rainfall of over 150" of rain and roof size, our catchment system is capable of harvesting over 200,000 gallons of free water a year. The tank has a liner approved by the FDA for storing food and water. The FDA has not approved a roofing material or gutters for drinking water but steel roofing and non-toxic gutters are used. The downspouts and other pipes to the catchment tanks are regular plastic plumbing components.
Just like municipal water, catchment water should be treated before being used. Here's what a typical system looks like:
The pump and pressure tank in the lower left of the photo pulls the water in from the catchment tank and pressurizes it. Water being held under pressure, the pump doesn't need to run every time a spigot is opened. It also ensures good water pressure even if you have all the showers, sinks, and toilets running at the same time. Two filters (one of them charcoal) remove impurities from the water. A UV sterilization unit kills any microscopic organisms that may have made it past the filters. Before the water is made into ice or consumed many people prefer an additional combination charcoal filter under the sink or in the refrigerator. Some homes use reverse osmosis or other treatment methods.
Because most newer homes have solar hot water, the water tank is 80 gallons or larger so extra hot water is stored for dark cloudy days. It has the ability to heat the water with electricity as a backup, using a timer to save power. However, we seldom run out of hot water and keep the electricity to it turned off. The system is capable of heating the water extremely hot- like to scalding. But because the system is not designed for that pressure it stops circulating the water through the solar collectors at a pre-set temperature. Any temperature above 150 will shorten the life of the tank, and the higher the temp, the shorter the life span. Ours is set at about 140 F. (most electric or gas home units are set at about 120). Because 140 degree water can burn the skin an adjustable mix valve mixes the hot water coming out of the heater with cold water before it enters the home so we don't get scalded. Ours is set at about 120.
Do people on catchment systems ever run out of water? We haven't, but it does happen. Several water delivery companies service the community by delivering a tanker load of water into empty catchment tanks or to fill swimming pools. Additionally, the counties provide free spigots where households can get potable water for drinking and other uses.
You may be wondering... what about sewer? Many homes without municipal access were built with cesspools, but building codes now require new construction to use septic systems.
For more information, the state of Hawaii publishes a water catchment guide: https://www.ctahr.hawaii.edu/hawaiirain/Library/Guides&Manuals/A_Guide_for_Rainwater_Catchment_Systems_in_the_Pacific_Portia_Franz.pdf