High intensity land use patterns and increasing pressure on water resources require effective stormwater management solutions in tight spaces. Rainwater harvesting programs collect runoff from rooftops, parking lots and other surfaces and reuse the water for such things as irrigation of gardens and municipal ballparks, washing patio furniture and lawn watering. Additionally, harvested rainwater when approved could be used indoors for non-potable uses such as toilet and urinal flushing. Indoor use designs are subject to review by the Plumbing Plan Review Program of the MN Department of Labor and Industry in accordance with the MN Plumbing Code, Chapter 4715 and would require pretreatment practices including filtration and disinfection. The effect is volume control, reduced flooding and erosion, and less demand for treated potable water. This fact sheet discusses the benefits of rainwater harvesting, highlights existing programs and provides conceptual designs for a variety of effective rainwater harvesting systems.
Rainwater harvesting programs serve multiple benefits. The collected rainwater can be used for purposes that would otherwise require potable, tap water. This reduces the cost of tap water to the owner and conserves potable water resources. All of the water captured and subsequently infiltrated (e.g. used for irrigation) removes 100 percent of the solids, nutrients, metals, pathogens and toxins that would otherwise have washed off, drained to the storm sewer, and then reached downstream waterbodies.
Harvesting and re-using rainwater decreases the impact of stormwater runoff to our lakes and streams; it protects the environment and minimizes localized flooding and erosion. It has additional benefits in urban areas, including, but not limited to, an increase in soil moisture levels for urban greenery. In addition, it can be used to meet regulatory requirements for stormwater volume control and water quality.
Programs designed to promote rainwater harvesting and reuse can incorporate any combination of the elements below.
Rainwater harvesting can be accomplished using rain barrels and/or cisterns. Rain barrels are typically small scale (25-100 gallons) and located at the downspout of a gutter system. They can also be linked to expand the overall storage volume (right). They are used to collect and store rainwater for watering landscapes and gardens or washing patio furniture. The simplest method of delivering water is by the force of gravity. However, more complex systems can be designed to deliver the water from multiple barrels connected in a series with pumps and flow control devices.
The total volume of storage available from rain barrels represents roof runoff from relatively small rainfall events, typically substantially less than one inch of rain over the surface. This is a small volume for a single rain barrel, but cumulative effects of rain barrels installed across a watershed include volume reduction and water quality treatment since typically the first half to one-inch of runoff contains the dirtiest water. During wet weather, there will likely be little or no storage available because of prior filling and little demand for irrigation water. If the ground can absorb it, consider discharging collected water onto vegetated areas between rainfall events to maximize rainwater capture and infiltration even if unnecessary for irrigation.