I was registered under this scheme when I lived in my house in London. Must say that I never ever came anywhere close to my water bill being the minimum amount which would have entitled me to assistance with paying the water rates.
However, did find it useful in other ways. Being registered, I became a priority when there was any sort of local water problem. One year, a local mains pipe burst and caused problems locally for a few days - the water board came to my house to ensure I was okay and to give to me about six large bottles of water.