As suggested in Gabrielle's article, rain is the best for watering. I have several containers that catch rain. The two main containers have lids, which is helpful in keeping the pesky mosquitos away. The main rain barrel, I add oxygenating water plants (Egeria najans) , water snails, tad poles and dragonfly larvae from the pond. This provides a mini eco system for your rain barrel. The oxygen plants do their job and produce oxygen for the tad poles and dragonfly larvae, and both love mosquito larvae for snacks. Occasionaly the larger dragonfly larvae will make a meal of the smaller tad poles. I keep this rain barrell full most of the time. The oxygen plants will also grow beautifully and you'll have a perpetual supply for your pond.
I usually empty the other rain catchers into the main rain barrel to keep it full. I also add a little frog ladder if the barrel is not full, so the toads and frogs can climb out when their time comes.
Is it safe to put those mosquito larva killing donuts in your plant rainwater supply? I've been breeding mosquitos because I'm afraid to put them in the water I will use on my plants. I have had store bought fish in there eating the larva, but they usually don't last more than a month and since they eat all the larva so fast, I have to suppliment with fish food. I'd love to get a green light on the donuts to save the hastle, but not at the expence of the plants I collecting the water for!
Thanks for your help.