EarthCare Society

Q. How many rainbarrels do I need?

A. This depends greatly on the combination of your roof area and personal preferences for outdoor irrigation uses, amount of garden, type of irrigation system connected to your barrel and intended use of your barrel system, which could range from very simple to quite complex.

Several tables have been assembled to help guide your choice.Table 1 shows average rainfall in Kelowna using long term climate normals gathered by Environment Canada. Kelowna is a semi-arid region of Canada with low precipitation and high summer air temperatures. Actual rainfall can vary from extremely dry such as the summer of 2003 to much wetter than shown in the table, but it still serves as a general guide. In the lowest summer rainfall month, August, the average rainfall is about 3.4 cm, which would yield about 700 gallons of water falling on a standard 1,000 square foot roof. (A 2,000 square foot roof would collect and shed twice this amount, or about 1,400 gallons). For August alone, we would need over 14 barrels (each barrel is 217 Litres) to collect all the rainwater! Most homes have four downspouts, so if the roof catchment area draining to each downspout were equal and accounting for about 20% leakage from roof gutters and efficiency loss of your connection system, each downspout would collect about 140 gallons. If you were really water conservation minded, you would need three to four water barrels connected in series at each downspout just to ‘harvest’ the rain from August! (By the way, if you were to collect all the rain and snow in a single year from the same 1,000 square foot roof, you would want to consider a 5,000-gallon tank polypropylene-lined corrugated tank).

In reality, however, most homeowners will be using rainwater as it fills in the barrel, and perhaps saving some as reserve for those periods of summer days without rain (the summer of 2003 was unusually dry!). Filling barrels before the typical pattern of dry, hot days is good preparation for these rainless periods. Now you need to estimate how much water you need. This depends on personal preferences, the size of your garden and types of watering system, such as by hand, drip irrigation or other. The best method is to actually measure the water level on the barrel before and after an application. Each barrel has gallon and litre markers for this purpose. You can also use some of the guidelines in Table 2 but keep in mind these are only guidelines and that every garden, person and situation will be slightly different.

Table 1. Amount of rainwater that could be ‘harvested’ by a standard roof size of 1,000 square feet
	March	April	May	June	July	August	September	October	November
Rainfall (cm)	1.69	2.56	3.9	4.07	3.69	3.36	3.27	2.5	2.13
Roof rain (Litres)	1570	2378	3623	3781	3428	3121	3038	2323	1979
Roof rain (gallons)	346	523	797	832	754	687	669	511	435
*If roof area is 2,000 square feet, then simply double the amount of rain that could be harvested.

Table 2. Guidelines for Determining Outdoor Water Use
Item	Volume of water
1 watering can	15 L (3.3 gal)
1 sprinkler full flow for 30minutes	550 L (120 gal)
Car washing (1/2 hour with hose)	550 L (120 gal)
10’ by 24’ garden	220 L (45 gal)

source: www.pacificcoast.net and others

A. Any stagnant body of water can grow algae if temperature and air conditions are right, including water in a rainbarrel. This is less likely in the blue barrel because less light enters, and in full barrels because there is less air. You can add algaecides or blue colour tablets, which are available at any gardening centre and you can fill and drain barrel water, which also helps keep algae growth down. Note that algae will not hurt your plants.

A. Mosquitoe larvae need about 9 days to hatch in stagnant water. The Watershed Rainbarrel is sealed, which helps prevent mosquito larvae from entering, but larvae can still possibly get into barrels from roof drainage or if other holes are drilled into the barrel top. Some preventive mechanisms include:

• Add a tablespoon of dish soap or ½ cup bleach to the water inside your barrel, or,

A. A simple method is to cut the downspout about one foot above the barrel height (remember to raise the barrel first on blocks!) with a hacksaw and install an elbow to guide water into the barrel. Downspout attachments are available at almost any hardware stores. Remove the top bung and be sure to place mosquito netting over the bunghole to prevent debris from entering.

Another method is to use a device such as the watersaver (see www.gardenwatersaver.com), which attaches to the downspout. With the watersaver, the extension allows you to put barrels in convenient locations such as around corners. Also, the small, nearly airtight connection to the barrel is good for keeping debris and mosquitos out. This device costs about $19.

Please contact the Canadian EarthCare Society for more information on purchasing a Rainbarrel

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Frequently Asked Questions Regarding Rainbarrels

Table 1. Amount of rainwater that could be ‘harvested’ by a standard roof size of 1,000 square feet

Table 2. Guidelines for Determining Outdoor Water Use