Renal failure - not urinating for a couple of days...

We have a friend with severe renal failure that does dialysis 3 days a week. We were just informed that he has not been urinating for a couple days. What is this a sign of? If you go to
http://www.fixmyparts.org/
you can see his bio and what he's up against. Can someone please check his bio and give me some suggestions on what he can do. He was drinking Alkaline Water for a little while, but he can only drink like 2 glasses of liquid a day.

Thanks Tweet