RENEWABLE SOURCES FOR WATER HARVESTING

There are a number of water sources that can be harvested for recycling. These fall into three general categories: Rainwater, Greywater and Groundwater. Each has its own set of advantages and disadvantages as well as implications for capturing, cleaning, storage and use.

RAINWATER SOURCES

Rainwater collection and storage, (also known as “rainwater catchment”), has been practiced for centuries by cultures throughout the world. Even in the U.S., most 19th century and early 20th century homes had cisterns that saved rainwater from roofs to use for washing clothes and watering gardens. In industrial countries, the practice had largely died away with the introduction of reliable modern water supply systems. This trend is now changing. Rainwater is free and mostly clean and requires less treatment than greywater, so it is an ideal source of water for harvesting.

For commercial and institutional buildings the two primary sources for rainwater catchment are the building roofs and parking lot areas. Because of the size of these impermeable surfaces in commercial buildings, the amount of rainwater runoff can be substantial, adding to the burden on municipal sewer and stormwater systems.

Parking lots generate large volumes of stormwater that are often contaminated with residue from road salt and automobiles. In most cases, this water runs to streams as untreated runoff or puts an extra short term burden on municipal treatment systems that has caused untreated runoff to enter lakes and streams. Many municipalities are now requiring new buildings to include plans to collect and manage this stormwater runoff so that it does not contribute to overloaded municipal systems. Wahaso can provide a system to clean, store and apply this vital water resource. Integrated cavern systems can prefilter the stormwater organically before it is stored, significantly reducing the filtration required in the active harvesting system.

To estimate the amount of rainwater your building will have available for harvesting, try out our Water Harvesting Calculator.

GROUNDWATER SOURCES

If your building will have a basement or parking area below ground level, then a sump system will likely be planned to remove groundwater from around and under the sub-ground areas. Of all renewable water sources, groundwater tends to be the cleanest and best suited to recycling – especially for irrigation. Traditionally, this water has been discharged into the municipal sewer or stormwater system – wasting its potential and further burdening the municipal system – a lost opportunity!

Whether your building is using active or passive harvesting, groundwater can easily be one of the water sources employed.

CONDENSATE AS A SOURCE

While cooling towers can be major consumers of water in a commercial building, they can also produce signficant amounts of harvestable water as they dehumidify the air inside the building at the cooling coils. In larger buildings, this clean source of water can generate a million gallons or more in a cooling season! For more information on cooling towers as sources and uses of harvested water, visit our Cooling Towers page.

GREYWATER SOURCES

Greywater, (also referred to as grey water, graywater and gray water) refers to water that has been used once in sinks, showers and baths. It is clearly distinguished from water from toilets – know as “black water”. Properly filtered and stored, greywater can be a valuable source of water to flush toilets and urinals or irrigate landscaping. Toilet flushes can account for 25 - 65% or more of the total water use in a commercial building, even when low-flush fixtures are used.

An efficient greywater system first requires a steady source of greywater. The most abundant source is showers in buildings with full time residents – apartments, dormitories, hotels, schools, etc. Restaurants with heavy dishwashing or clothes washing use may also produce suitable quantities to support greywater harvesting. Office buildings generally do not produce enough usable greywater to warrant the cost of a system.

When there is an abundant supply of greywater, it can be a more reliable source of water for flushing toilets than rainwater. The amount of shower and sink usage generally ties to the amount of toilet use in a building, so there is almost always a balance in supply and demand for greywater.

There are significant implications for the use of greywater. Greywater harvesting requires additional treatment versus rainwater and always an active system versus a passive system of collection and storage. This is due to the heavier load of soaps and organic particles that is carried in greywater. The additional filtering and sterilization requirements can add 50% to the cost of a system vs. rainwater harvesting systems. As a relatively new form of water conservation, many communities have not yet set standards for greywater processing and storing with some communities banning its use outright.

Water Harvesting Solutions has extensive experience in developing and managing greywater systems for commercial properties. Our processes remove all organic materials so that the stored water is cleaned to near-potable condition. This eliminates any issues with odor or color, and meets the needs of most municipalities. As part of our services, we can research and advise on the appropriateness of greywater harvesting in your community as part of your total water management system. We can also recommend resources for working with your municipality to set standards for greywater collection, filtering, storage and use.