Ditto on the clean containers and fresh water! We used to use a 5 gallon cooler with PVC pipe that fed into the coop and had the watering cups attached but I had a problem with algae growing in the cooler and I know there was some growing in the PVC pipe so I went back to the old way. I have a Hanging 3 gallon waterer but I fill it up every 2 days. I have 11 chickens and it lasts for a couple days before it needs changing.
Put a couple of copper fittings in the water or some pennies made before 1982. After "82" they were made with a copper coating. If your waterer is in the sun, maybe you could move it or put something over it to shade it.
"If your Lincoln Memorial penny has a date before 1982, it is made of 95% copper. If the date is 1983 or later, it is made of 97.5% zinc and plated with a thin copper coating. For pennies dated 1982, when both copper and zinc cents were made, and best way to determine their composition is to weigh them."
Not sure what type of waterers you have, but an enclosed, fully opaque waterer kept in a shady spot should have few issues with algae growth. I have never actually had to clean out my adult chicken waterers other than a simple quick rinse (the chick waterer is not opaque and gets slimy fast).