Economy of rain-barrel

I've wondered about the economy of rain-barrel. Utility Kingston is selling a 200L rain-barrel for $30. However, the water-rate for Kingston is about $0.6546/m^3. So a simple math ($30/$.6546*5) shows that I need to fill up the rain-barrel about 230 times in order to recover the cost of the rain-barrel. It certainly doesn't rain 230 days in a year in Kingston. And I have to cut the downspout.

However, it is the right/green thing to do. I'll probably do it.

just my 2-cents.