Q: I have a rain barrel. The water has developed a green film. Is it alright to use it to water my plants?

A: The green film is just algae growing on the nutrients that washed off your roof and into the barrel. The water is perfectly safe to use on plants. If you like, you could add 1/8 teaspoon (or 8 drops) of household bleach for each gallon of water to disinfect it.