When placing multiple water wells next to one another, they are capped at 1/n the refill rate where n is the number of well placed in close proximity (right next to one another). So for instance, I put 4 wells up next to one another and even upgraded them. Regardless of seasonal or terrain bonuses, they are each capped at 25% (1/4 production). While a nearby business was constantly draining one well and tapping another, the two other wells continued to fill. When one of them reached the 300 water limit, it stops filling, obviously. The problem is that the other wells are still reduced to 25% rate even though one of the wells is already full.
It is my opinion that a full well should not tax the rate of other wells because it is not filling any further. It may also be interesting, if not as simple for most players, if the refill rate was higher the emptier the well was and slows down as the well gets fuller, but with a minimum rate that it will continue to fill by. In this way, the penalty for nearby wells can be calculated from the rate they fill rather than the number of wells near by and this would make more sense.
The only reason one might put several wells together in a cluster is because we don’t have pumps and water towers. We also cannot store water in any storage building or market. So clusters are the only way to store large vats of water for sudden fire outbreaks, or when the breweries are in full production. When they are stalled waiting on more grains or when the stock limit has been reached, the wells will fill back up. These buildings chug water. I can see maybe the barns and other animal buildings needing water troughs being filled as well as their winter food storage.