I know this sounds particularly counter-intuitive, especially coming from a water conservationist, but it is precisely for that reason that I will not irrigate my garden from my rainwater tank. Here’s why:
I installed a rainwater tank in my garden in Noordhoek on the Cape Peninsula. I had this romantic notion of collecting rainwater from my roof, and using the water on the garden during the many dry days that Cape Town experiences during the summer. I rubbed my hands in anticipation after the first rains and felt very proud of my conservation efforts.
I bet you can see the problem: a 5 Kiloliter tank fills up very quickly during the winter months, leading to excess water overflowing into the stormwater drain. What a waste, I thought. But since this was mid-winter, and we were getting lots of rainwater on the garden, I didn’t need any additional water at that time. Not a problem, I thought, I will wait until summer and make good use of that full tank of water.
Problem number two, I can see you counting off on your fingers: one week into the dry season, and my tank is now empty and I am thinking back longingly to the time the tank was overflowing. So for the rest of the summer, my beautiful, romantic rainwater tank sat empty.
Summary: useless in winter, and useless in summer – only useful for one week in spring.
So what is the solution? How do we take advantage of the winter rainfall without impractically building a bank of 20 rainwater tanks?
Here it is: use the water collected in the rainwater tank in your house as your primary source of water, backed up by municipal water during the dry season. You will use almost no municipal water during the winter rains, and you will use the same amount as usual during the dry season.