I collect rainwater into 150-gallon tanks under my greenhouse benches for use in watering. Sometimes the water is held for two to four weeks before use and can get pretty rank. Is there anything I can do to minimize the growth of algae in the water? I use a quaternary ammonium product in my swamp cooler and I am not impressed with the results. - John Hyatt
Rainwater properly stored should be able to be held for a long time. If the tanks are under the bench and not covered, they can easily be contaminated by runoff from plants above and the combination of nutrients and light are ideal conditions to support algae. Proper handling of rainwater includes the following:
* The collection area must be kept clean. In Bermuda, most houses depend on rainwater for all their needs, so when the rainy season starts, they let the first few showers wash away the dust and dirt from their white roofs before the start of collection.
* The storage tank must be covered to prevent any contaminants from entering. Once contaminated, it is no longer rainwater.
* The storage tank should also be relatively light-proof, as any light will promote algae growth. -
Thomas Sheehan, PhD