The Big Island of Hawaii is basically a huge volcanic rock in the ocean. We do have a water table, in fact there are trillions of gallons of water at about sea level in a big lens that goes from shore to shore. However, within a few miles of the shore the water is brackish. By the time you get inland far enough to have good clean water, you are up over 1,000 feet on the side of a mountain; a mountain of solid rock. It costs about a million dollars to drill a thousand foot well. Because of the cost, and because most places have ample rainfall, Hawaiians just run the water from their roofs into a big tank for storage and then pump it back into the house through a filter with an electric pump system made for this purpose.
The old systems used redwood tanks from one to ten thousand gallons or more. Now they use above ground swimming pools or special metal tanks with liners up to 60,000 gallons. The pools are covered with shade cloth to keep bugs out and some people build a metal roof as well to keep leaves off the cover and catch a little more water. The water is pumped into the house by an electric pump activated by the change in pressure when you turn on the tap. Also, a captive air tank in the system will keep the pressure more or less even as the pump cycles between 40 & 60 psi. For areas without electricity, a 12 volt pump is used that runs off the batteries of a solar system. I used to drive home and hook the pump up to my car battery. My old redwood tank leaked so bad I put a pool liner in it.
There are activated charcoal filters to improve taste and take out odors and there are ultraviolet light filters to kill bacteria. When I first moved here all I had was catchment water, there was no filter, and we drank the water freely.
I have friends who live in Opihihale on catchment water who even have a regular swimming pool. (The swimming pool is to swim in and is chlorinated. The catchment tanks are above ground and covered; you don’t want to swim in your drinking water anyway!!:-) Occasionally, during drought conditions, they have to buy water from a tanker service. Cost is about $300 for 5,000 gallons which can last as much as three months. I have another friend who lives up in Waiono Meadows high above Kailua-Kona. He has a 60K tank. He will never have to buy water!!
Call the Water Works in Kainaliu for installers and parts, etc. If you have an ultraviolet filter it’s safe to drink the water. Build a roof over your tank and hang the cover from the underneath of the roof to keep it off the water. Best way is to have 4 grommets in the center of the cover and run a rope through and then up to a pulley hanging from the underneath part of the roof. Then pull up the cover into a tent shape and tie off the rope to the outside somewhere. Add gutters to the roof for extra catchment area.
Here is a great link to a pdf that tells about catchment systems: www.ctahr.hawaii.edu/oc/freepubs/pdf/rm-12.pdf