How much daily water intake to prevent dehydration?

It's hard to get H2o into dad, he says he drinks but I see the same level in the glass all day long, he drinks the ensure I buy him, He was drinking milk but now not much due to the chocolate ensure. I buy him zero water no sugar and he may drink half of one a day per the ones left in the fridge. He does drink a couple of cups of coffee a day but that is not hydrating.
He goes out with his friends and from his food receipts, he has a beer or wine.
That is only 2 times a week.
Other than that I can't get him to drink much more. He has had 2 UTIs in 3 months with one hospital stay but still doesn't get it.

?

I am on dialysis 5 days per week. My fluids are restricted to 26 ounces per day from all sources. Usual amount on dialysis is 4 to 6 eight ounce cups per day. This recommendation comes NIH, Mayo Clinic, etc I was started on dialysis when my GFRreached 26. I have Stage 4 chronic kidney disease. I have been under nephrologist care for over 35 years.

If you look into it the recommendation to drink 2 litres of water every day is more myth than fact. If her urine isn't extremely concentrated and foul and her bowel movements are normal then she is fine.

https://www.mcgill.ca/oss/article/health-nutrition/water-myth

I had kidney failure because of something i drank..had to go on dialysis for 3 months until it cleared up.. During that time I could only drink 4 ozs a day to give my kidneys time to rest and recuperate.. . everyone on dialysis can only drink 4 0z a day it wasnt me because i had a kidney injury...my nepheroligist said he didnt understand where that 64 oz a day came out for anyone?

I'm thinking an 86 year old kidney can use some rest. if you can look at the color of her urine really dark or non good. everything else, not blood ok.

no medical training, just observation from when i was on dialysis. think about it more as resting tired kidneys. lots of older people at diaylis center. many older people first organ to fail is kidndeys then it cascades to rest of organs(my grandmother for sure started at her kidneys)(my other grandma was from heart failure...extra fluid makes heart pump more)

just my opinion, there are other things you can worry about. but it is very good she has a child that is concerned about the details.

Maximum age for dialysis is 80.

low fluids cause constipation and muscle soreness. tough to differentiate from arthritis and lack of excersice. dry lips look for those signs more than what she is drinking.