Rainwater Harvesting Systems
Rainwater harvesting systems redirect and store water for both potable and non-potable uses including drinking, irrigation, laundry, hygiene and toilets. Most rainwater collection systems are designed to capture rainwater from roofs and store it in tanks. System designs range from a simple barrel at the end of a downspout to a complex potable or multiple end-use system using a large cistern. These systems can be incorporated into new construction or existing buildings.
The six basic components of a rainwater harvesting system are:
- Catchment area, typically a roof — galvanized metal coated with nontoxic paint is most common; other options include concrete, terracotta tiles, slate, polycarbonate and fiberglass.
- Gutters and downspouts to channel water from roof to tank.
- Leaf screens, first-flush diverters and roof washers – components that remove debris, dust and other contaminants before rainwater reaches the tank.
- Storage tank, or cistern – installed above or below ground; made of corrugated steel, concrete, polyethylene or fiberglass.3
- Delivery system — gravity-fed or pumped to the end use.
- Treatment/purification — filtration and treatment are needed to make the water safe to drink. Treatment options for potable systems include ozonation, UV, and chlorination.
Materials used should be nontoxic and non-leaching. Public water can supplement the system only if back flow devices are installed for water supply protection.
Implementation of a rainwater harvesting system involves:
- Deciding on the intended use of the water
- Estimating water demand for the intended use – reduce demand, and ultimately system cost, by implementing water efficiency features
- Determining whether sufficient water will be available to meet demand – based on frequency and volume of rain and on catchment surface area
RATIONALE
Rainwater harvesting systems reduce non-point source pollution such as pesticides, fertilizers and petroleum products that end up in rivers and groundwater. As decentralized water systems, they contribute to restoration of stream flows and habitats. Integrated on-site water capture reduces the waste and environmental disruption involved in centralized water distribution systems. Rainwater catchment systems can replace use of potable water for irrigation, which is the largest use of fresh water in the United States according to the USGS.7 At home, the average person uses 80 to 100 gallons of water per day, mostly for toilet flushing, followed by bathing.6 Very little of the potable water used in the home is consumed for drinking and eating. Implementing water-efficient technologies in combination with a rainwater harvesting system can eliminate or vastly reduce use of public water supply.
SUSTAINABILITY PRINCIPLES
- Development of integrated water and watershed management plans
- Integration of land use plans and water management plans
- Promotion of creativity and innovation in water use efficiency and water conservation
- Minimization or elimination of the introduction of non-point source pollutants
- Differentiation of potable uses
EFFORT REQUIRED
- Build and work closely with design team to incorporate BMPs
- Evaluate and reduce current water usage
- Estimate projected demand for the intended use
- Adhere to any regulations that may exist for these systems in your state and/or municipality
- Install system, including building retrofit where necessary
- Develop and follow operations and maintenance schedule
- Educate building occupants and visitors
BENEFITS
- Reduce non-point source pollution
- Reduce water bills
- Reduce volume of stormwater runoff, thereby lessening erosion and decreasing load on storm sewers
- Increase plant health - Plants thrive when irrigated with stored rainwater
- Reduce demands on centralized water delivery systems, especially during drought or dry season
- Reduce need for costly expansion of centralized water delivery systems
- Provide isolated properties with alternative to groundwater or high tap fees
- Obtain credits for green building rating systems such as LEED™
- Reduce need for spending on site storm water controls
RISKS
- Responsibility of operations and maintenance is on the owner
- Insufficient rain to meet demand
- Contamination of water due to improper design, installation, or maintenance
ACTION AGENT(S)
Contractor, land use planner, facilities manager, developer, architect, engineer/hydrologist, landscape architect
COST
Most non-potable systems range between $10,000 and $30,000 installed, not including the roof. Potable systems or very large commercial systems will likely have a higher cost range. The largest expense is the storage tank, ranging from $0.50 per gallon for large fiberglass tanks to up to $4.00 per gallon for welded steel. Professionally installed gutters range from $3.50 to $12 per foot. Pre-filtration equipment ranges from $50 to over $800. Pump costs run from $385 for the low-end pump to more than $1,000 for combined high-end pump and pressure tank. For potable systems, filtration/disinfection can cost up to $1,000 or more. A simple rain barrel system for watering plants will cost around $200.
