Have you ever wondered why after heavy rainfall supply from rivers goes down?

This is because when there is heavy rainfall the water isn't clean enough to use. We have to wait for the dirt and leaves (that have been churned up) in the water to settle before we can use it.

And by the time the water settles, and is good enough to use, the river may have already receded.

Long periods of drizzly rain are best for river supply.

Although a big downpour may result in higher river levels, it does not always result in greater supply of drinking water.

And that's why we have to use water from the Waiwhetu aquifer and our storage lakes, to make sure supply meets demand.