The idea of collecting water from the roof of our home elicits some primeval response related to survival – we need water, we need security, it is natural to want to be able to grow things. The crazy suburban fiesta of the past 40 or 50 years has removed us from the realities of food and survival, with centralization and expansion of everything being the theme of the era. Larger schools, hospitals, farms, malls, roads, and water treatment have all had massive impacts on the way we interact as a society – possibly more than any of the technological advances we’ve made in communications (although an argument can be made that these are intricately related and symbiotic in nature). Centralization of services and expansion of living space has been the name of the game.
But through all this effort, cracks are starting to show where the systems are weak. One of those areas is the harvesting of rainwater on the average lot. Considering the world water issues with aquifers diminishing and climate change induced surface water sources drying up combined with higher water demands from consumers – all sources of water need to be considered in many parts of the world – rainwater, greywater and recycled effluent as appropriate. I’ve discussed all of these here on UrbanWorkbench in the past, but today, I’d like to examine the recent popularity of rain barrels in North America.
Jerry is being sustainable about his efforts with his newly installed rain harvesting system because it saves the water agency electricity from not having to pump 20,000 gallons of water to his home anymore.
Collecting this much rainwater significantly reduces stormwater runoff and erosion problems. That’s 20,000 gallons less rainwater that could get contaminated by the time it gets to a stream or an underground aquifer.
Recently I had the opportunity to directly respond to a suggestion that the municipality subsidize rainwater barrels, “like another municipality” (Castlegar). Here is a summary of my response…
Debunking Rainwater Barrels
It sounds like good PR (which we need to keep building!), but there are technical issues, some thoughts:
- As a City we would need to budget for this.
- Many homes in Rossland are not equipped to use these – gutters are required and many homes do not have gutters installed.
- If used regularly, each 240L rainbarrel can be expected to save 2000 litres of water a year – about $0.80 a year. (Yes it is 2000 litres of water, but there are easier ways to save this amount).
- These will not supply enough water for gardens to water regularly despite restrictions, after a single rain event, the average household would be able to water a vegetable garden for half a week before the rainbarrel is empty. We probably average 40-50 mm of rainfall a month over summer which typically comes in 5-10mm storms. Off a 1000sqf roof area you would need 4 or 5 barrels to capture one 10mm storm, assuming it were empty.
- More plastic products may not be a great solution to water conservation, even if these are not PVC – there are many sides to sustainability.
- The “First flush” off a roof is dirty from dust, bird droppings etc – and this first water should be disposed prior to commencing collection of roof water. Such systems are not readily available in Canada at this stage.
- Bottom line, these have a negligible effect on water conservation compared to other initiatives- a reduction of about 0.02% (I’m running off memory for the numbers). If we wanted to lead in this field we should be procuring not 240 litre tanks, but 2000 litre tanks or bigger – which would allow a buffer for capturing water even if it is not empty.
- 900,000 cubic meters supplied from water treatment plant
- 200 cubic meters saved by 100 rain barrels
- Rainbarrel Size 240 litres
- Average Garden Size 10 sqm
- Watering requirements for vegetables – 50mm per week (?)
Comparison to Water Meters
If we spent the same amount of money on installing water meters – this might procure and install say 40 meters. Assuming we can get an average reduction in demand from these 40 residential homes of 15% over a year, this would be about 80 cubic meters per household, 3,200 cubic meters – 16 times more effective at saving water than rainwater barrels.
Suggestion to Municipalities
Don’t get caught up in the latest “green fad”. There are easier ways to save water. If it is determined that this is a priority for a municipality, I’d suggest limiting municipal funding to tanks of over 2000 litres at a minimum for the simple reason that they are the most useful just about anywhere in the world. Local research may be able to provide an optimum size of tank per square footage of roof catchment.
Do you have a rainwater barrel? If so does it get used?