Rooftop rainwater harvesting is the collection, conveyance, storage, and distribution of natural rainwater for non-potable applications. Instead of storm water immediately running from roofs into sewers, it gets collected and stored for later use, such as:
Rainwater harvesting is ideal for large commercial and industrial buildings, especially ones with expansive parking lots, and can be retro-fitted to existing buildings or integrated into new building designs. A rainwater harvesting design starts with siphonic roof drainage, through which rainwater is diverted from the roof to an on-site storage tank. This stored water is filtered and can then be diverted both indoors and outdoors to be recycled for toilet flushing, facility cleaning, irrigation, etc. Not only does the facility save water consumption costs, but it also reduces storm water runoff on the site, which can provide leverage for a company looking to attain building permits.
How does it work?
Systems are designed to meet each facility’s individual needs, depending upon roof size, water demand, intended usage for the gathered water and the projected amount of water to be collected.
No matter what the particular application, the core components of a typical rainwater recovery solution are the same. They include the following:
- Collection - comprised of the catchment area (i.e. roof) and conveyance system (i.e. gutters and downpipes)
- Holding Vessels - cisterns, tanks or other suitable storage container
- Roof-wash system (optional) - usually the first 10-20 gallons of rain are diverted from the cistern to improve water quality and minimize debris build-up
- Delivery System - the delivery system consists of pumps and piping (e.g. water is withdrawn from the holding vessel by a pump that delivers the water to sprinkler heads for irrigation)
- Filtration (optional) - to remove particulate and contaminants for the downstream application. This can be simple or comples, depending on the requirements and applicable healt and environmental regulations
- Water Cost Savings - Rainwater harvesting reduces consumers’ utility bills. The water is essentially free; the only cost is for collection and use.
- Added Property Value - Rainwater recovery solutions also add value to your property. In times of drought the advantages are clear. But, even when there is an abundance of water, having a system in place that is not dependent on municipal water supplies can be a determining factor in your landscaping and grounds upkeep.
- Simple Distribution – With rainwater recovery systems, the end use of harvested water is located close to the source, eliminating the need for complex and costly distribution systems.
- Taxpayer savings - Large-scale incorporation of rainwater harvesting helps utilities reduce the summer demand peak and delays expansion of existing water treatment plants, as well as investment in development of new water sources.
- Pollution control - As storm water runs off a property, it normally washes contaminants such as fertilizers, pesticides, and petroleum products into the storm drainage system, and ultimately into rivers, lakes, reservoirs, and groundwater. A rainwater harvesting system captures water before it runs into the storm drainage system, thereby decreasing such non-point source pollution.
- Erosion and Flood Control – By reducing the volume of storm water, rainwater harvesting systems can thereby lessen the occurrence / impact of erosion, and decrease the load on storm sewers. Harvesting also combats flooding by reducing peak flow from high rain events.
- Water Conservation - Use of rainwater reduces demand and reliance on limited groundwater supplies and surface sources, such as reservoirs. It also allows for groundwater recharge, which is critical in light of ever increasing population and water demand.
- Better Quality of Water - Rainwater is valued for its purity and softness. It has a nearly neutral pH, and is free from disinfection by-products, salts, minerals, and other contaminants. The zero hardness of rainwater helps prevent scale on appliances, extending their use. Additionally, rainwater eliminates the need for a water softener and the salts added during the softening process; and plants tend to thrive under irrigation with stored rainwater.