Graywater Reuse and Rainwater Harvesting

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Graywater Reuse and Rainwater Harvesting

Graywater refers to the reuse of water drained from baths, showers, washing machines, and sinks (household wastewater excluding toilet wastes) for irrigation and other water conservation applications. Contrary to common belief, graywater is not a benign product – it may contain bacteria and other potential pathogens.

Graywater is of lesser quality than tap water, but generally of higher quality than blackwater, or water from sewage systems. Water from the kitchen sink, garbage disposal and dishwasher is considered blackwater in some states because of high concentrations of organic waste and the difficulties of reusing this water safely.

The most obvious advantage of domestic graywater use is that it may potentially replace other water used for landscape irrigation, although many interests are now advocating the use of gray water for toilet flushing. Filtered graywater is most suitably used for subsurface irrigation of landscape plants – not for ediable plants. Not only does its use on landscapes conserve treated tap water, but graywater may also benefit plants because it often contains nutrients such as nitrogen or phosphorus.

Graywater use may offer financial savings to already overburdened municipal sewage treatment facilities because graywater use diminishes sewer flows, thereby lessening the need to expand such facilities. However, diminished sewer flows may have a downside because graywater use can result in insufficient sewer flows to carry waste to the sewer plant.

Graywater systems vary from simple, low-cost systems to highly complex and costly systems. A common (but illegal in most states) method for reusing graywater is to drain the washing machine directly onto outside vegetation. Sophisticated systems treat graywater prior to disposal using settling tanks and sand filters in order to remove solids and pathogens. (Note: settling tanks and filters will not remove pollutants that are dissolved.)

Rainwater Harvesting

Rainwater harvesting is the process of intercepting storm-water runoff and putting it tobeneficial use. Rainwater is usually collected or harvested from rooftops, concrete patios, driveways and other impervious surfaces. Buildings and landscapes can be designed to maximize the amount of catchment area, thereby increasing rainwater harvesting possibilities. Intercepted water then can be collected, detained, retained and routed for use in evaporative coolers, toilet flushing, pet and car washing, indoor plant watering, pet and livestock watering, and for lawn and garden irrigation.

Rainwater harvesting systems vary from the simple and inexpensive to the complex and costly. Typically, these systems are simple, consisting of gutters, downspouts, and storage containers. Directing rainfall to plants located at low points is the simplest rainwater harvesting system. In this system, the falling rain flows to areas with vegetation. Inexpensive rainwater storage systems commonly make use of above ground containers such as a barrel or plastic tank with a lid to reduce evaporation and bar access for mosquito breeding. Any container capable of holding rain dripping from roof or patio can be used as a rainwater harvesting system.

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