My plants prefer rain water over rested* Maynilad water. We collect rain water for the plants and switch to regular water during dry months. We used to just place 2 drums where water would drip from the garage roof. It took awhile to collect water. When master plumber Rod saw our set-up he suggested a way to collect water better.
Rod fixed the roof gutter and the downspout. Some of them were not draining properly. Since we don't really have space for another water tank, he suggested to collect water from the downspout. We originally planned to collect from the garage roof, but the downspout that was installed was not the round one. Rod said it'll be better to collect from the main roof!
He added a tube to one of the downspouts. We can easily open it if we need to collect water and close it when the drum is full. We have two drums and Sweetie just moves the water when the extra drum is empty. My plants have been so far happy and we sometimes use it for cleaning. Actually, I noticed that the feral cats prefer to drink rainwater than faucet water. They know it's fresh water :)
Of course, we always cover the drums to make sure that mosquitoes don't lay their eggs in it. We also wash the drum every so often. We usually wait for awhile before we open the pipe to let the rain wash out roof debris. Sometimes there's some silt at the bottom of the drum. We empty the drum and wash it with Domex before we fill it up again.
For our future home we plan to have a dedicated rainwater tank. It'll be used mainly for plants and outdoor cleaning. Rod said it can be switched to collect Maynilad water during dry months. It's useful since we've been able to keep our water bill low. :)
*Water left in a pail overnight before you use it for watering plants