To keep your rainwater from stagnating, use your harvested rainwater as frequently as possible. Also, clean your barrels regularly, especially if you notice algae growth or impurities. Use dark-coated and food-grade barrels to prevent contact with sunlight that fosters algae growth and mosquito breeding. Moreover, clean the screen filters where rainwater enters before reaching the barrel, and have the lid of your container tightly covered. Furthermore, clean your gutters and roof regularly so that no large debris will enter and may clog your downspout pipes.