Here are the two types of waterers I've used that have never had algae in all the years I've had them. The first one is a plastic planter actually, I just plugged the holes with food grade silicone (because I liked the rustic look). The commercial waterer, I have two sizes of - a 1 gallon and a 3.5 gallon. I only use those when I have chicks, so they don't drown in the planter bucket. I have a retired baby bottle brush hanging by the waterer, and I give it a quick scrub with the brush every few days when I change the water. The watering station is in full shade, to keep it cool in the summer (the white things in the planter waterer are ice cubes, because it's HOT over here).
