RENEWABLE SOURCES FOR WATER HARVESTING
There are a number of water sources that can be harvested for recycling: Rainwater, Stormwater, Greywater, Groundwater and Condensate. Each has its own set of advantages and disadvantages as well as implications for capturing, cleaning, storage and use.
What is rainwater? 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.
“Rainwater” by definition is precipitation that is collected from relatively clean, above-ground surfaces – usually rooftops. Because rooftop rainwater has minimal contamination, it is an ideal source for harvesting. In commercial buildings, the large rooftop areas can often collect enough rainwater to meet all the non-potable uses like toilet flushing and irrigation.
What is stormwater? “Stormwater” is defined as precipitation collected off outdoor ground level surfaces. This water may be contaminated by automobile oils and fluids, unknown chemical spills, and nitrates and pesticides from landscaping. In commercial buildings, it is usually the parking lots that throw off vast amounts of stormwater during a rain event. – and can be millions of gallons per year. Unmanaged, stormwater can run off into streams and rivers with its contaminants. At the very least, it must be conveyed miles away for treatment in a municipal stormwater system using energy and resources.
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. Property owners scan pend hundreds of thousands of dollars to filter and detain stormwater and then release it slowly back to the local municipality. Ironically, these same property owners then buy back municipal drinking water to flush toilets and irrigate their landscaping! Wahaso can provide a system to clean, store and apply this vital water resource. Integrated cistern systems can prefilter the stormwater organically before it is stored, significantly reducing the filtration required in the active harvesting system. Click here for more information on stormwater harvesting.
To estimate the amount of rainwater your building will have available for harvesting, check out our Water Harvesting Calculator The folks at Wahaso can also provide a custom analysis of your supply and demand. Contact us.
What is greywater? Greywater, (also called grey water, graywater and gray water) refers to water that has been “gently used” in sinks, showers, baths and light industrial applications and has not yet been treated. 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. Some manufacturing facilities can harvest water used in their manufacturing processes if it is not heavily loaded with contaminants. 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 if it is to be used inside a building or for spray irrigation. The additional filtering and sterilization requirements can add 50% to the cost of a system vs. rainwater harvesting systems. However, because daily supply and demand are in balance with a greywater system, the cost of storage tanks can be significantly reduced vs. a rainwater harvesting system – bringing the total system cost into the price range of a large rainwater system.
As a relatively new form of water conservation, many communities have not yet set standards for greywater processing and storing. Local codes often restrict the use and storage of greywater – but the codes are meant to protect public safety from the contaminants in untreated greywater. Once the greywater has been treated, its definition becomes “onsite treated non-potable water” and falls under a different set of usage and storage guidelines.
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. Read more about Greywater Harvesting Systems.
What is groundwater? 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.
What is condensate? While cooling towers can be major consumers of water in a commercial building, they can also produce significant 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.