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Water-neutral pools capture every drop

Establishing access limits to the California water coffers has led some residents to come up with creative conservation ideas. The state is no stranger to drought and has already taken major steps to limit water consumption. 

For example, during the last major drought of the ‘90s, they retrofitted virtually every toilet in Southern California, installed low-flow shower heads, and other low-flow plumbing fixtures, resulting in a 20-percent decrease in water consumption today, despite an increase of 5 million more people. 

Jeffrey Kightlinger, the general manager of the Metropolitan Water District of Southern California, says that with this drought, the change we should make is outdoors. More than simply allowing a lawn to go brown, the water district wants residents to remove it, and the MWD is willing to put its money where its mouth is: the district is offering $2 a square foot of lawn removed. To date, about $60 million has been spent, and MWD expects to do $100 million by the end of this year.

The water district is also offering a $50 rebate for residents who install a rainwater harvesting system, and city utilities departments offer additional incentives. For example, the San Diego Utilities Department offers $1 for every gallon of rain barrel storage capacity, up to 400 gallons. Many other California cities are offering similar incentives. Rainwater harvesting is a great way to contribute to California’s conservation efforts, particularly for pool owners, who will no doubt come under fire in the months ahead.

For pool service professionals, encouraging the purchase of and installing rainwater harvesting systems is a smart approach to the drought. The concept of rainwater harvesting is simple. All that is necessary is to capture water falling on the roof and direct it to a storage tank. Harvesting systems are available of varying levels of complexity and price. By some estimates, a professionally installed harvesting system could run between $3,000 and $10,000 for a single family home.

The amount of water that it is possible to collect is based on the amount of rainfall and the square footage of the roof. Specifically, the volume is equal to 0.6 gallons per square foot per inch of rain. That means that 600 gallons could be gathered from one inch of rain on a 1,000-square-foot roof. To get an idea of the total amount of water that could be collected a year, Los Angeles gets an average yearly rainfall of about 15 inches. During the 2013-2014 drought year, however, Los Angeles saw just 6 inches of rain. Nonetheless, with a U.S. average roof of 1,600 square feet, it would be possible to collect about 5,700 total gallons of water during a drought year. That’s not bad!    

The main components of a rain harvesting system include: 

The roof

Gutters and downtake pipes

Filters and first flush devices

Storage tank(s)

Delivery system

Rain water falling on the roof is collected by rain gutters and directed down through a filter to remove grit leaves and dirt. When it rains after a long dry spell, roof tops will have plenty of air pollutants and the first flush device diverts early rain water away from the storage tank, which can be above or below ground. Finally, some sort of delivery system is needed for accessing the water. Sizing the system is based on how much water can be captured, how much water is needed, and cost. The size of the tank needed, based on an Australian pool and spa association’s recommendations, can be found in the accompanying chart.

The storage tank is the most expensive part of the system. For the largish volume of water needed for a pool, tanks cost anywhere from $500 to $2,000. Rain harvesting systems can include pump systems for rain water catchment. This is necessary if the storage tank is below ground. Aboveground systems are less costly to construct and can be gravity fed, although booster pumps may still be needed, and a filter should be added, regardless of the setup. 

Normal pump systems include a pump, a pressure tank, a pressure switch, and a check valve. The catchment pump system draws water from the pump, pressurizes it, and stores it in a pressure tank until it is needed. The one-way check valve between the tank and the pump prevents the water from returning to the tank. When the spigot is turned on, water is delivered under pressure. The subsequent pressure drop activates a pump switch, which turns the pump on so that water is continually delivered. 

Pumps provide better service if there is a large pressure tank on the system. This extends the life of the pump since the pump will turn on and off less.  Installing a rain harvesting system can be simple, or more complicated if additional filtration and disinfection is desired. For example, floating extractors are an often overlooked part of rainwater catchment systems. These solve the problem of where, inside the storage tank, the water is pulled from. Depending on its mass, debris in the storage tank tends to either float or sink. Pulling water from the middle of the tank provides the cleanest water, and a floating extractor makes this possible.

Other systems incorporate UV sanitation or membrane filtration like reverse osmosis. Rainwater harvesting is practiced all over the world, and can even be made safe for drinking when fine filtration and disinfection measures are taken.  Using rainwater harvesting for pool water is part of the measures required for having what the Australians call a “water-neutral pool.” The Australians introduced the concept during their 9-year drought from 2003-2012, when their water reserves were drastically depleted.

The core of a water-neutral pool requires just three elements:  a rain collection tank for refilling the pool as needed; a pool cover to reduce evaporation; and a backwashing minimization system to reduce water loss from excessive backwashing. When implemented properly, these tools can not only save water: they can actually produce water. 

A multidecade study in Melbourne found that over a non-drought, 30-year period, a water-neutral pool could produce an average of 22,000 gallons of water. During their drought, the pool could still produce 6,000 gallons of surplus water. These numbers should be very reassuring during California’s water crisis. There is little doubt that the pool industry will struggle during the coming months. Creating the elements needed for a water-neutral pool is just one step that the industry can take to both do its part, and stay afloat.

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