Add fresh water daily by placing your hose end in the bottom of the trough and allowing the water to run over the top for about five minutes. This will displace old water with new, clean water. About once a week (or whenever the water appears dirty) empty the trough, scrub it with bleach, rinse it thoroughly and refill it. If you have a very large trough, you may wish to add a couple of ounces of household bleach per fifty gallons of water to discourage the growth of algae.