No, it's just commonly used as a herd health treatment and putting it in the water makes it easier than giving individually. Most medications for agricultural use will commonly be given in water if they can be taken orally. I don't need to do herd health (most of of don't, with a handful of backyard chickens) because I only have 6 chickens! It's much more accurate to give medications directly based on the animal's weight than to put them in food/water, where you have to estimate consumption, and a sick animal might not eat/drink a normal amount. Some medications do need to be divided into two or three daily doses, but if it can be provided orally in food/water, most medications are safe directly. And most antiparasitics are given as a single daily dose.
What I listed was the oral (i.e. direct) dosage. Dosage for adding to water and food were also provided, based on volume of food or water. Dose actually doesn't seem high based on the volume of water they drink and the water dose of 9.6ml/gallon; it worked out to about 0.15ml per chicken at the high end, so just under a ml total for all of them, and they drink just under a pint of water in a day (when they don't spill half of it!). Volume-wise, that correlates. That amount of medication is so small, about 2 drops, it's so easy to just give it to them, and I know they're getting what they need.
If anyone cares, reference is the Exotic Animal Formulary by James W. Carpenter.
