Drowning rats was the most effective solution that I have seen and it was by chance. To ensure that calves were not born too early in the spring, we confined the bull to a pen in the barn that was only used for him. The rest of the year the pen was empty. The next winter when I was forking manure out of the barn I went ahead forked the bull's pen too. In the pen was a 55 gallon barrel that had ben cut down as the water bucket for the bull and the water level was about foot down from the top. Since I was cleaning, I dumped the barrel over with the intent of rinsing it out and refilling it. Once dumped, bodies of several dozen rats sloshed out with the water. Disposed of the rat remains, rinsed out the barrel, then set it back up with the water level about a foot down from the lip. From then on, I made sure that the water in the barrel was always down enough from the lip that the rats with have to lean way in to get a drink.
Good luck wit your water traps
Good luck wit your water traps