Alternate Water Sources

One way to reduce treated water demand is to substitute an alternate water supply for an existing demand that does not need treated drinking water. Using stored rainwater to irrigate plants is an example of this concept. Most onsite alternate water sources in residential and non-residential settings are non-potable (unsuitable for human consumption). The most common alternate water sources are rainwater harvesting, stormwater harvesting, and graywater systems.

Blow-down Water

Water that is drained from cooling equipment to remove mineral build-up is called “blow-down” water or “bleed” water. The cooling equipment that requires blow-down is most often cooling towers, evaporative condensers, evaporative coolers, evaporative cooled air-conditioners, and central boilers (both steam and hot water).

Condensate Water

When water vapor in the air (often described as humidity) comes into contact with a colder surface, the water changes from a gas to a liquid and collects onto the cold surface. This water vapor in the air that becomes liquid is referred to as condensate.

Graywater Recovery and Treatment Systems

Graywater (aka gray water or grey water) is generally defined as untreated wastewater that has not come into contact with toilet waste, kitchen sink waste, dishwasher waste or similarly contaminated sources. Graywater includes wastewater from bathtubs, showers, and bathroom wash basins, clothes washers and laundry tubs. The capture, treatment, and reuse of graywater not only yields usable water that would otherwise be directed to the sewer, its use on the landscape and for car washing is generally not subject to the typical watering restrictions that are sometimes imposed by local jurisdictions.

Graywater Systems

Graywater (aka gray water or grey water) is generally defined as untreated wastewater that has not come into contact with toilet waste, kitchen sink waste, dishwasher waste or similarly contaminated sources. Graywater includes wastewater from bathtubs, showers, and bathroom wash basins, clothes washers and laundry tubs.

Rainwater Harvesting

Probably the original alternate water source, rainwater harvesting dates back to pre-historic times. Current rainwater harvesting typically features rain barrels or cisterns. Many water utilities now offer free or price-discounted pre-fabricated plastic rain barrels to residential customers.

Reverse Osmosis Discharge Water

Reverse Osmosis (RO) filters use membrane technology to filter impurities such as minerals, calcium, chloride, sodium, and chlorine from the water. The systems require periodic backwash to clean the filter. This discharge water is usually directed to the sewer drain line, but it can be recovered and used.

Stormwater Harvesting

Stormwater harvesting refers to rainwater collected from non-roof surfaces, such as parking lots, hardscapes, and landscapes surrounding urban buildings. Managing stormwater in urban environments has reached near crises levels in some cities, as urban sprawl grows and landscapes are paved over with non-porous materials such as concrete and asphalt.

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