This article is about outdoor, residential systems. For larger, multi-residential or commercial integrated systems, see Rainwater harvesting
Rain barrels are an above ground form of rainwater harvesting, typically used in residential settings. The precipitation flows from the roof, to the guttering and down the downspout before being diverted to the rain barrel for storage.
Rain barrels are an ideal technology for:
- Individual homes, where the owners can make good use of the water to irrigate a garden
- Retrofitting single family home neighborhoods
- Areas with mandatory downspout disconnection programs
The fundamental components of a rain barrel system are:
- A catchment where the rain lands, this will usually be a rooftop,
- guttering and downspouts to channel the rainwater,
- screens or filters to remove leaves and other large debris,
- a rain barrel to hold the collected water,
Additional components may include:
- a tap or faucet fitted to the barrel,
- a hosepipe or other irrigation system.
Traditional rain barrels require a high degree of owner compliance to perform as a reliable stormwater management control strategy at watershed scale. To overcome this limitation, electronically monitored and controlled rain barrels are a new adaptation on the market in Ontario. This system forecasts rain and automatically discharges the contents of the rain barrel to a designated infiltration area of the property in advance of the storm.
Place in the Treatment Train In most cases the catchment area will be the roof of the building and the rain barrel will be the first interception of water from the downspout. Planning questions:
- How many downspouts does the roof have?
- Will more than one barrel be required?
- Do the downspouts require reconfiguration?
It is recommended that an overflow strategy be part of designing a rain barrel system. Excess water should be directed away from the property foundations. Suitable discharge points for overflow include: a rain garden, a french drain, or the base of a tree.
The water in the barrel will remain fresher for use if leaf litter and other debris excluded. Screens can be installed on the eavestroughs, in the downspout, or at the top of the cistern. These types of screens are not designed to capture small particles and chemical pollutants. However, this fine material is usually first to wash off surfaces at the start of the storm. A first flush diverter is a simple, automated, mechanical device which prevents this first 'dirtier' part of the stormwater from being stored. Screens, filters and diverters should be in easily accessible locations, so that they can be inspected and cleared of debris periodically.
Roof catchment area can be estimated using one of many online digital maps. e.g. Distance can be measured on Google maps by right clicking on the desired start point.
1 mm of rain landing on 1 m2 of roof top produces 1 litre of water to store.
So a 5 mm storm on a 75 m2 roof would require 375 L of storage volume.
Rain barrels are readily available in pre-formed plastic in a variety of sizes, ranging from 150 to 200L (typical) up to 500L.
- modular systems to increase total storage capacity,
- slim designs to fit small spaces,
- aesthetic designs for high profile locations,
Many people choose to reuse or recycle a container as a rain barrel or cistern. Re-purposed containers should be screened to prevent mosquitoes from breeding, and should be opaque to prevent algae from growing.
The effectiveness of rain barrels depends heavily on whether the homeowner will utilize the stored water. The use of rain barrels (190L) across a watershed of 100 residential units has been modelled for a number of U.S. cities. In Philadelphia and Milwaukee (reflecting the most similar climates to Southern Ontario) the use of rain barrels for irrigation only, provided an annual stormwater reduction of less than 2%.
The Ontario building code (OBC) requires only that water collected from rooftops be "free of solids" for irrigation use in an external system such as a rain barrel. There is a draft of CSA B805 draft currently under review. The scope of the document includes single family dwellings. But the guide is still under review and may not account for rain barrel systems when officially published. (comments made in reference to draft v. 2, on 1st June 2017). Research in warm climates (Texas and Greece) has demonstrated that first flush diverters improve the chemical characteristics of the harvested rainwater. However, the use of diverters does not prevent the development of pathogens in stored water. Rain barrels are not typically accepted to provide any quantifiable water quality treatment beyond that achieved through runoff volume and pollutant load reduction.
Many municipalities run schemes to provide homeowners with subsidized barrels. In some places barrels can be purchased from around $50. See list below. Additional items such as filters, screens or hoses may cost extra. Hardware stores carry a wider range or products to suit all kinds of space constraints, aesthetic concerns, or budgets. Outdoor barrels for the residential market can cost up to $300, these have larger capacity and smart sensors.
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