What's right for you?
Rainwater harvesting systems can be broken down into two basic categories: Active and Passive. With active systems, we are trying to capture, convey, store and eventually distribute water for a specific purpose such as flushing toilets, irrigating or even drinking. Passive systems, on the other hand, seek to manage the movement of water to encourage retention in the landscape, evaporation or infiltration to groundwater. Many systems integrate both active and passive elements. Even the biggest tanks must be able to provide for overflow during Coastal BC's rainy winter months. Why not try to hang on to this water rather than sending it down the drain?
Active rainwater harvesting
A rain barrel is a simple example of an active rainwater harvesting system. Rain falls on a catchment surface, usually a roof, and is conveyed through gutters and a downspout to the barrel where it is stored until needed for irrigation or another purpose. Use of the water depends on some kind of distribution mechanism. For a rain barrel, this could be as simple as a watering can.
As we ask more of the system, its complexity must increase. Our rain barrel, for example, would not be sufficient to offset much of our water consumption and would only be likely to hold a small fraction of the runoff from the roof during a typical storm event. If we want to capture more of that water and hold on to it, we need to use bigger tanks or cisterns. These would have a larger footprint, potentially making it necessary to place them further away from the house or even underground. They may also need to be supplied by multiple downspouts to take advantage of more of the roof's capacity for catchment. Given expanded demands on the system, we would want to ensure that we filter the water before it is stored and provide adequate protection for system overflow. We may also need a pump to get the water where we want it to go and maybe filtration and disinfection if we need the water to be potable.
Active systems, depending on their scale and your needs, tend to be more costly to purchase and install, but they allow greater flexibility in how and when you use the water. They can be combined with passive elements to allow you to take advantage of overflow rather than discharging directly to the storm sewer or other drain.
It is important to remember that, on its own, an active system with full tanks will not reduce stormwater flows during a rainfall event. Active systems can, however, be designed to discharge water slowly to the stormwater system or a passive system component. This will help to moderate peak stormwater flows.
Passive Rainwater Harvesting
Passive systems utilize landscape features to reduce runoff and encourage retention of water in the landscape or slow infiltration to groundwater. They can be created to handle runoff from impervious surfaces like roofs or driveways or can reduce overland water flows that result when soils become saturated. Examples of passive systems include rain gardens, vegetated swales, permeable pavement and infiltration beds.
Although often overlooked, passive systems can be a great option for homes and businesses that do not have a specific need for stored water. They can be designed and sized to accommodate weather patterns in your area and, depending on your site, may allow you to retain a large amount of water in your landscape.