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Big Island Off Grid Living: Harvesting Rainwater with a Catchment System

  |  Resources for Big Island Residents, Sustainability and Off-Grid Living

My husband and I are “on catchment.” We drink and shower with water we catch from the sky.

Living on the east side of the Big Island presents an opportunity to consider using rainwater catchment for your water needs. On Hawaii Island, there are somewhere between 30,000 and 60,000 people using catchment systems. When purchasing a home, potential buyers can be comfortable with houses that use a catchment system if they do a little research first.

We live near a water tank that the Hawaii County Department of Water Supply maintains as “municipal water” to many of our neighbors. We have watched the County workers test and treat the water through the years. It is comforting to know that homeowners can treat their catchment water much the same way that these workers do.

A Brief Overview of Catchment Systems

Corrugated catchment tank with cover

Corrugated catchment tank with cover

Catchment system design is important for water quality and the amount of effort required to maintain that quality. Water tank covers protect the water from the sun and from intrusion from animals. Other important considerations are filtering and treating the water before it goes into the tank and also before it goes into the house.

Here’s how a typical system works:

Water is collected from a roof and is then gravity-fed into a holding tank (or series of tanks) which usually holds 8,000 – 12,000 gallons. Some systems use a first flush diverter and tank inflow filter to clean the water before it goes into the tank.  This helps minimize contaminants that can come from the roof.  When my husband and I purchased our home, the catchment system was already built. We added a passive first flush diverter and a simple filter (a nylon stocking!) for the water before it enters the tank.  These two simple improvements have significantly reduced the amount of unwanted matter entering our tank.

Pipe arches supporting a mesh cover keep it from sagging into the water

Next, the water pump sends pressurized water to the house. Before the water enters the house, it is filtered again in several ways.  At our house, it is filtered in two ways. Coarse filters are used for water for showers, toilets and sinks. For drinking water, we filter it first with coarse filters, then with ceramic filters to remove any microorganisms, and then with UV filtration to sanitize the water. A filtration system can be designed for the entire home or only for specific points of service.

On a monthly basis we treat our collected water by adding Clorox Ultra Bleach and we replace the nylon stocking that contains debris with a fresh one. That process takes only 5-10 minutes. Periodically, we replace the course filters and the UV bulb and clean the ceramic filter.

With a catchment water system, my family can control how our water is collected and treated. Control over our water system (even the pipes the water flows through) gives us great comfort about our water quality. Having spent half a lifetime on municipal water systems, we can testify that our catchment water tastes far better than any municipal water we’ve ever had.

Because it’s impossible to discuss the myriad of issues surrounding rainwater catchment systems in this short blog post, you may want to see this excellent guide on rainwater catchment systems developed by the University of Hawaii, Department of Natural Resources and Environmental Management, College of Tropical Agriculture and Human Resources: Guidelines on Rainwater Catchment Systems for Hawaii.

More information is available from the Hawaii Rainwater Catchment Systems Program at University of Hawaii’s College of Tropical Agriculture and Human Resources website.

Photos used with permission, courtesy University of Hawaii College of Tropical Agriculture and Human Resources.

Contact Shirley “Charley” Black at 808-896-1208 or visit her bio page here.

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