The National Ground Water Assn. (NGWA) announced that ...
One of our most important natural resources for the sustainability of life is water—and it is running low. As a result of a combination of reduced water supplies and increasing human populations, water supplies in various geographical locations throughout the U.S. are unable to adequately meet population needs. This, in addition to the green movement and the increasing importance of sustainability, is causing people to turn to harvesting rainwater.
There is essentially one way to collect rain and that is by catching it, and one of the most common ways to catch rain is from a roof of a home or building. A distant second is to collect water from storm water runoff that races down pavement, but that tends to collect unwanted contaminants like oils and trash.
Once the catchment method is determined, a conveyance system is used to bring the rainwater to one of two storage methods: above- or below-ground rainwater storage tanks.
The more popular catchment system is an aboveground system. What it often comes down to for the homeowner is cost, and a belowground system can cost more than four times as much as an aboveground system. In most cases, cities, government entities and the commercial building industry have the financial resources for belowground systems.
The primary use for collected rainwater is outdoor irrigation such as potted plants, gardens, lawns or swimming pools. Rainwater is not potable; however, it can be if a series of filters are in place prior to the rainwater entering a residential plumbing system. A typical treatment train of filtering and disinfectant devices can be screening, sedimentation, filtration, ultraviolet light exposure, chlorination, anticorrosion additives and reverse osmosis.
Because most of the rain-collection systems installed in the U.S. are primarily nonpotable and aboveground, this discussion will be focused on the components of an aboveground rain collection system.
Where to Begin
Before building a rain harvesting system, first find out how many gallons of water on average the home-owner uses outdoors during the summer and winter months. Next, find out how much rain the roof can collect on an annual basis based on average rainfall amounts in the area and the square feet of the footprint of the roof.
An aboveground, nonpotable rain-harvesting system consists of several components such as a catchment area, gutter guard filter, conveyance method, roof washer, rain storage tank, air gap, water level indicator, overflow and a natural gravity flow water faucet. A water pump may be unnecessary as long as the storage tank and the area to be irrigated is on flat ground and if a drip system can be used.
Installing a fire hydrant to the rain storage tank is admirable if there is not one located near the home. Typically, a fire hydrant can be installed, according to local county building codes, if the tank has a storage capacity of more than 2,500 gal and if there is no fire hydrant within 100 yd of the home. Adding a fire hydrant is a considerable added expense, but that is overshadowed by the potential devastation that can occur from a house fire.
The catchment zone is the area in which raindrops land and are collected. Using a roof is an ideal catchment method because they are generally sloped and have a gutter to channel the rainwater to a downspout. For a nonpotable system, it is not important what types of roof shingles are on the home.
The use of a gutter guard as a first-stage filter for filtering out leaves, pine needles and roof sand grit is important. For example, Gutterglove Gutterguard is made of a 316 stainless steel mesh filter supported by a hardened anodized aluminum support frame. The mesh has several thousand holes per square inch; therefore, nothing gets through but dust and rainwater.
The next component is the conveyance system, which is simply an array of schedule 40 polyvinyl chloride (PVC) pipes to get the rainwater from the gutter downspout to the rain tank. If the rainwater has to be routed underground, near or under a driveway, use schedule 80 PVC pipe for extra strength.
A conveyance system suspended above the storage tank that brings the rainwater from the roof to the top of the rain tank inlet is called a dry system. A conveyance system that routes the rainwater from the roof to the rain storage tank via underground piping is a wet system, meaning when there is rainwater in the tank, the conveyance piping will always have water in it.
A roof washer is used inline with the conveyance system to divert the first several gallons of rainwater from the beginning of each rain event away from the rain tank. This washes off the roof without letting this dirtier rainwater enter the tank. The cleaner rainwater then enters the rain tank automatically without the use of electrical parts.
When choosing a rainwater storage tank, a careful evaluation of the manufacturer’s specifications should be read. Tanks should have resins that meet the U.S. Food and Drug Administration guidelines, and where applicable, should be NSF-approved.
The rain tank should be equipped with an air gap to allow air to leave when the tank is being filled and to allow air to enter when the tank is being emptied. This is especially important when installing a fire hydrant because most building codes require at least a 6-in. air gap.
A water level indicator is a nice added feature to have on the tank. There are many different types out there, so search carefully. The tank will also need an overflow at the top for when it becomes full and it is still raining.
Installing a brass water faucet for access to the rainwater near the bulkhead on the bottom of the tank allows the rainwater to exit the tank through natural gravity flow. Make sure you put a sign on the faucet that reads “Rainwater – Do Not Drink!”
Near this location you can also install a pump to push the water in any direction desired throughout the property.
If you are in earthquake areas of the country, you can also use flexible safety connectors that allow the tank to move due to ground settling and earthquakes.