Criticism, like rain, should be gentle enough to nourish a man's growth without destroying his roots.
- Frank Howard Clark
Recently I received a well-considered email from a resident asking whether or not the City of Kamloops had considered subsidizing rain barrels as a way of conserving water. The new barrels are durable and come with a spigot at the bottom that is designed for a standard garden hose.
It's a thoughtful idea and some gardeners do use collected rainwater. A couple of serious gardeners I know use collected rainwater for their "better" flowers because they feel that rain water is better than chlorinated tap water for more delicate plants.
They probably have a point.However, from a pure cost perspective a 45-gallon barrel is about (rounded up) 200 liters.At a metered rate of 65 cents per thousand litres, using a full barrel of rain water would save you about 13 cents.
Let's presume a largish roof covering an area of 150 square meters (1,500 square feet or so).We get a total of 270 mm(10.6 inches) of precipitation in an average year so we should get 40.5 cubic meters (8,500 gallons) of water off a roof presuming the barrel collected every drop and every drop was used.At 65 cents per cubic meter you might save $26, which would be significant.Of course, the problem is that our barrels would produce water at times we didn't need it.Most of the spring runoff would be wasted because we would have no outside use for the water when the snow melted.
A review of a climate chart for Kamloops can tell us how much rain falls in a given month for a typical year. Environment Canada publishes this data on their web page (which I am using for this illustration).From the beginning of April to the end of September we would expect to see 160.6 mm (6 inches) of rain.Our rain barrel should then collect 24 cubic meters from the roof in this illustration or around $15 worth of water.Still significant, but not as much as before.
Now, as we all know, the rain does not always fall in regular amounts at regular intervals.In a storm event the barrel might be overflowing and then go weeks without seeing any rain.Still, I think it would be reasonable to assert that you could save about $10 per year in water use by using a barrel in this situation.Of course, if you were collecting rain water you would likely be doing a lot more careful hand watering, which would greatly reduce your water use generally so there could be some other dividends from people using rain barrels as part of their watering regime.
Of course, there are other real world factors to consider. First, I am assuming that all the rainwater off this theoretical roof is being collected and drained to a single point.At my own home there are five separate places where the eaves drain to the ground so a single barrel would not work for me.
Most homes would need at least two rain barrels to collect most of the water that might drain from the eaves of their home. Finally, it takes some effort to integrate watering with a rain barrel along with regular watering. That said, gardeners taking the time to collect rainwater are probably committed to using the water whenever they can. These careful gardeners are generally not the problem in the first place because they use resources intelligently and don't over water.
Now, take a place like Toronto, which charges about $2.10 per cubic meter and gets 436 mm (17 inches) of rain in the same warm months our 150 square meter roof would collect over 65 cubic meters of water saving $137 or so per year. Even after accounting for overflows, a Toronto gardener would be well advised to invest in a rain barrel (or two).It would likely pay for itself in the first year or two of use.
I truly appreciated the letter writer's suggestion and it caused me to spend some time to think it through. I forwarded his idea with my response to David Duckworth, our director of Engineering and Public Works. Being a curious engineer, David was one step ahead of me, having used a rain barrel at his own home to see how effective it was.
He managed to fill the barrel a couple of times over the warm months and used the collected water for his outdoor flower pots. Considering the barrel cost around $100 and he saved 26 cents worth of water, it didn't make much economic sense. He did go on to state that his family uses a rain barrel mostly because it feels good to utilize Mother Nature's resources as wisely as possible.
In many climates a rain barrel can make a lot of sense and I wouldn't argue against anyone choosing to supplement their watering with collected rainwater. However, I'm not convinced there is sufficient grounds to merit public subsidy of rain barrel purchases.