Having that exact problem in my current game. Bakery at 5%- because of water shortage even though a well is adjacent. I was wondering what affects well production, sometimes they are not 100%. Am building a second well for bakery to see if that floods the bakery hehe... It even has it's own 2 farms. Wow, do you normally need 2 wells and farms for one bakery?
wells are working at 100% if there is some water left in their working radius. But as this radius is very small they hav quickly used up all the water. After that they work at a 66% chance I think.