Rain Water Harvesting

Rain water harvesting (RWH) is a relatively easy way to obtain clean water in areas such as Northumberland County. We receive, on average, 44 inches of rain each year and a catchment area of only about 1300 square feet can provide enough water for one extravagant consumer. In many places in the world people have obtained, and continue to obtain, their domestic water this way. There are three components to a rainwater harvesting system: 1) a catchment area, 2) piping to remove some contaminants, and 3) a storage container. Water can be distributed from the storage container by gravity or by means of a pump.

1) Perhaps surprisingly, any sort of roof and gutter system is a satisfactory catchment area. Water from rain runs off very quickly, and most of the contamination accompanies the "first flush", or the first few gallons of water (which is also true of impervious cover such as paved driveways and parking lots). Obviously the roof needs to be maintained more than would normally be the case. Washing several times a year, to remove things like bird droppings, and keeping the roof and gutters free of leaves and debris, are the only kinds of maintenance normally required, but they are necessary.

2) Piping between the catchment and the storage container directs the water, but also removes particles and discards the "first flush". Inclined screens of several sizes, separated by several inches, with the coarsest screen on top, can efficiently remove particles all the while discharging the water vertically into the pipe to the tank. Window screen is typically the finest (bottom) screen, and its function is not only to remove fine particles but to keep mosquitoes out of the storage container. An easy way to remove the "first flush" is to place a vertical pipe, say about 4 inches in diameter, beneath the screens. A valve is placed in the bottom of the pipe, which is barely opened so that water drips out. Somewhere near the top of the vertical pipe, a "T" is placed, and the horizontal run of the "T" is connected to the storage tank. When rain begins to fall, the vertical pipe fills with the "first flush", and only when the water level reaches the "T" can water discharge directly into the storage container. When the rain stops, the vertical pipe empties slowly through the valve at the bottom, and is ready for the next event. Obviously this is an arrangement which requires maintenance. The screens must be checked frequently to be sure they are not clogged or broken. More importantly, the valve at the bottom of the vertical pipe must not become clogged or else the pipe will remain filled with water and the "first flush" will flow directly into the storage tank. Simple though this system is, it will not withstand sub-freezing temperatures.

3) Any material can be used for a storage container, but there are two requirements. First, the container must have a sufficiently tight lid so as to prevent mosquitoes from entering. Ideally the lid should be large enough so the tank can be easily cleaned. Secondly, the container must be light-tight. If light enters the container, algae will grow in it and the microbial activity which results might contaminate the water. Placing the container underground protects it from freezing in the winter, shields it from light, and hides it from view, but is costly and requires that the water be pumped.

RWH is a relatively inexpensive option for both potable water and water for other uses, such as watering plants. People who use large amounts of water for irrigation in the warm months should seriously consider RWH as a way to reduce their consumption of groundwater. Rainwater is better for the plants than is our deep groundwater, which has a very different chemistry from shallow groundwater. Additionally, we need to conserve our deep groundwater, which is being depleted at an unsustainable rate. Potable water from RWH may need to be further filtered, through activated charcoal for example, or otherwise treated (by irradiation with ultraviolet light, for example), and these options are easily (although not necessarily inexpensively) accomplished with a standard pressurized water system. RWH is not maintenance free, and installation should be undertaken only if a willingness exists to monitor and maintain the system on a regular basis, especially in the fall when leaves are abundant and in the winter when sub-freezing temperatures occur.

Several good sources of information can be found at:

http://www.rdrop.com/, http://www.ci.austin.tx.us/waatercon/. http://www.fao.org/ag/AGL/aglw.