Water Pills Aren't Full Of Water?

Mom is recovering well. She is breathing a lot easier and hopefully the rest will pass soon. We found out that Grandpa had more complex issues. Grandpa was diagnosed with having excess water surrounding his heart. I hear this isn't good but aren't we made up of 90% water? Anyhow, they gave him water pills to help reduce that. He was supposed to urinate the excess water but supposedly an enzyme or hormone caused a backflow from the kidney which sent the toxin into his bloodstream. This has been alleviated but not explained as thoroughly as it should be. He's feeling better after spending the weekend worrying about his body falling apart. I'm only hoping that this was just a little scare but anything can happen. More importantly is getting his spirits up. This is a big weight off my shoulders and let's hope they stay light for a bit longer.