Not that long ago we paid a total of $2.64 per 100 cubic feet of water used, now it is up to $3.9162 per 100 cubic feet. That is a 50% increase in just over two years. Our summer period water and utility bill from the City of Victoria came to almost $500!
I decided to look into getting a rain barrel to see if I could reduce our summer time use of water. The prices I found for 300 to 400 litre barrels was about $100 to $200. Being an analytical guy I thought I would do some math and see if it would make any difference financially for us.
Working with a 400 litre barrel, this is 14.125 cubic feet, or in water rate terms $0.55 worth of water. For me to save enough water to pay for the cost of the barrel, I would have to fill it up and use it 180 to 360 times to cover the cost.
So how many times would I expect to be able to fill this barrel in the period from May 1st to September 15th, roughly the limits of when I need to water around here? The barrel would be getting water from about 400 square feet of roof and using the data from the UVic weather network for my neighbourhood, I could come up with an approximate number times I could fill it. Looks like about 8 times is what would be a 'normal' year, if I am lucky that could be as high as 12 times, but I am going use an average of 8 times a year. It would take 23 to 46 years for me to save enough water to pay for the initial cost of the barrel.
So how expensive would my water rates have to be to make the rain barrel a useful investment? If I am willing to allow for a seven year return on the investment, and this is longer term than 90% of people consider worthwhile when considering home efficiency improvements, I am looking at water rates of $12.50 to $25 per 100 cubic feet of water, three to six times as much as I pay now.
The normal pay back time that makes the majority of people choose to do something is under three years. At three years the water rates would have to be $30 to $60.