Borax is very good for animals and humans alike in the right dose. It does help arthritis - joint problems. One word of CAUTION! I started taking a very small amount diluted in water ( 1 tbsp per gallon water) I took 1 tsp of water a day. Being 2 years into menopause, no periods, I had a "period from hell". It does affect your hormones. I stopped taking it. Will wait a year and try again.
I have used Borax in my RO water at a rate if 1/8 teaspoon per gallon and also add a pinch of grey salt. In my entire immediate family, there are 19 canines and 5 cats. All of them have been drinking this water for 21 months and we have not had any issues.
In fact, our older dogs seem to move less painfully. Hope this helps :)