Q: I plan to buy two sixty-five gallon rain barrels to collect spring rainwater. In July when everything is dry, I will use it to water my fruit trees. How can I keep the water from becoming stagnant? 

A: Add 1/8 teaspoon (or 8 drops) of household bleach for each gallon of water to disinfect it.

But I think your trees need more water than your barrels can economically provide. They may need twenty gallons each per week in the dead of summer. If the barrels cost $50 apiece, you’re investing $100 to save $1.30 of water. Let’s say you use the barrels each summer for 10 years and you collect and use 1000 gallons each year. If water prices are $.01 per gallon, you’ll only earn back your initial $100 in ten years. I suggest you use the barrel money to buy a Treegator (click for sources) and municipal water.

Here’s something I wrote a few years ago:

ECONOMICS On the face of it, collecting rainwater seems like a good idea. Southface Energy Institute calculates that the roof of a two thousand square foot house could yield forty thousand gallons of water in a year. With metro water rates near one cent per gallon (including the typical sewage charge) residents of this house could save four hundred dollars if they collected every drop of rain.

COLLECTION However, rainfall is not evenly distributed throughout the year. It is concentrated in winter and spring, when the water usually is not needed in the garden. Summer thunderstorms yield lots of water but you would need eight hundred gallons of storage to hold the rainfall produced by a one inch gullywasher falling on our example home. Unless you’ve had the forethought to install a true cistern, managing sixteen fifty-gallon drums of water is beyond the skill of most gardeners.

Even if you are content with a single rain barrel, the water must be screened before it enters the barrel. Leaves and pine needles are easy to exclude for Master Gardener Theresa Schrum but she finds that pine pollenmakes a goopy mess inside her barrels each spring.