99% sure the water purifiers only produce so much water at a time (a very low rate) that is both the same AND shared across all purifiers and the size of the purifier just determines how many they can store (small - 2, normal - 3, and industrial - 5).

The production rates listed on their crafting menu (like the industrial purifier saying it produces 60/hour) are entirely fictitious and mean absolutely nothing.

IE: Whether you have one small water purifier or ten industrial water purifiers, your camp will only produce like two purified water in the next ten minutes (made up rate, I don't recall what the real rate is, this is just an example; its definitely not the advertised rates on the crafting menu though). The ten industrial purifiers won't produce purified water any faster.

But in that same example, after those ten minutes, your one small purifier will be full with the two purified water it produced and will not produce anymore until you empty it. Whereas the industrial purifiers will continue producing water until all ten are filled with five waters each.