just wondering if anyone can give me advice on my dogs diet and water intake , ozzy a gsd is 10 months old and has been on beta puppy since 3 months , i took him to the vet this week yo get neuted and the vet refused to do it saying he was very under weight , he was 28k , to be honest i knew he was a little and i was shocked when the vet said how under weight he was , anyway we started to talk about his diet and water intake  , ozzy has around 2-3 litres of water a day and the vet seems to think that he is also drinking to much he was also concern about ozzys poo every so often he poo becomes quite sloopy for a few days but then fine , before he does anymore tests he asked to change his diet to the royal canin for 2 weeks to see if he puts on weight ,now he has been on this for a few days and i have seen a difference already , he poos twice a day now where as before it was up to 6 times a day also he seems to be calmer on the food but the worry is his water intake is still the same , so really i need to know is this to much water he is drinking the vet seems to think it is!!!!
hope someone can help!!!!!!

2-3 litres does sound a lot, even for a large breed dog pm a dry diet.  It may be that the drinking has become a habit. BUT excessive drinking can also be a sign of stress.........  One of my dogs always drinks to excess around firework time :(

there was a chart I found somewhere that calculated a dogs water needs on dry food as being about .25litres per 5kgs body weight.  Mine drink about a liter or more if it is warm a day and they are 20kg. 

I would expect your boy to drink at least 1.5litres.  Some dogs just enjoy drinking, but excessive water intake can be a sign of diabetes and kidney disfuntion among other things.

You might find your dog doesn't drink as much as you think.