Horses can drink between 25-50 liters a day normally. Is he drinking more than this? Has it changed recently or has he always been a thirsty boy? I have to do a lot to encourage my old man to drink so as long as your guy is within normal limits, I'd consider it a blessing that he regulates himself so well. If it is more than that, or has recently started to increase, or if you're noticing urination abnormalities, I'd say a basic CBC and chem panel are in order.
They are blood tests that your vet can run for you. I'd say keep an eye on her general health, and watch her for changes. She may just be settling in. If she seems depressed or lethargic then you might be concerned but some horses just drink more than others. How much do you think she drinks. I know you said you "fill it up" but what is "it"? 50 gallon tank? A bucket? Hard to judge without knowing how large your water bin is.
That's not too bad... I had a gelding that got dehydrated and impacted because he didn't drink ENOUGH. Check her poo... if she is having diarrhea I would be concerned as well. I agree with Tealamutt too.. how big is the water bin? 5 gallon bucket?
I agree...the size of the bucket or tank will help...
In the summer my mare easily drank 1/4 of a 50 gallon tank each day...I'd rather have a horse drink alot, than not enough...there are so many things that can go wrong if they don't drink enough!! If they drink alot they may just pee more, but I'd rather have that than an impacted horse!