Thanks for the posts everybody. I did switch everyone back to the bottled water about 4 days ago and will keep them on it. We will be selling our house in the spring and we'll set up a water filter system at our new home, wherever that may be.
The thought about the food allergy is interesting because I did mix a new food in with their regular dry food 2 weeks ago. The standard mix that they used to get was Medi-Cal Preventive dry mixed half and half with Wellness Healthy Wise. The pet store was out of the Healthy Wise so I decided to try another Wellness and got the Salmon kibbles instead. But for the past 3 or 4 days though it has just been Preventive because I ran out of the other. I guess I didn't think of it because it never occurred to me that all of them would have the same allergy. But I guess it's possible. I suppose the easiest thing will be to see how they do on their regular Preventive/Wellness HealthyWise mix and see if it clears up. If not, it has to be something other than the food and water.
Maybe something in their litter has changed. We use the same kind as we have for years but maybe the content has somehow changed. We use a scoopable kind called Kitty Scoop made by Purina.
I'm still wondering about a Paddy connection because it would tie in with his overgrooming in that one area, maybe it is itchy and not behavioral? Also, he does have a few funny bumps on him in different sizes. There are never any increasing bumps, just the ones in the exact same spots. One of them is the size of a dime while others are quite a bit smaller. I asked the vet to look into his records from his old family and the file shows that they brought him to the clinic once years ago for alopecia on his inner thighs and the vet made notes about 'pustuals' (spelling?) on his skin. The family didn't opt for any kind of treatment. The couple of little bumps on his skin don't seem to bother him and after what happened with Charlie and having his lump removed and losing him I'm extremely wary of messing with it.
I think I'll google a few words like 'bumps, pustuals, chewing paws, losing hair, reddish skin" and see what I come up with.
Can you see rings on cat's skin with ringworm?