I have an 11 year old dog that we found when she was about five months old. She started seizuring around the age of two. About once a week, occasionally more often. We installed an R.O. water filter system for ourselves and realized within a couple of months that our dog had stopped her seizures. The only difference was the water! She now seizures only about six times a year.
We did notice that she started seizuring after eating "bacon strip" dog treats, and other treats with food colorings, etc. We went back to plain dog biscuits and she's fine. She must be chemically sensitive. I shared this info with her vet who said she would pass this info along.