I suspect with free choice hay, your cows are indulging in more hay than they need for survival. Just a guess, but my cows would eat more if I left it out. My point is, the more dry matter the cow eats, the more water she's going to need to digest that dry matter.
If your cows are in good condition without being overly fat, then continue with your feeding program.
Either way, as Dun said, they should have access to all the water they want. If you restrict their water intake, you are asking for digestive problems.
The water founder theory may come from times when cows didn't have water available all the time and weren't raised under the controlled conditions most of our cows live under now. If a cow has been without water for a prolonged period of time and is dehydrated then, yes, introduce water gradually until her system is back to normal. Other than that unusual circumstance, give the cows all the water they want to drink.
I think I remember reading where cows drink about 10 to 15 gallons per day, so 5 gallons would be far under their needs.
By the way, make sure your cows also have free access to good mineral & salt.
> I have 3 cows that are going to
> calf in March. They weight around
> 1300,1250 and 1150 pounds. Have
> all the hay they want and feeding
> them 2 pounds of steer feed each a
> day. They are like drinking 125
> gal. of water every 2 days, give
> or take 25 gal. It's a 175 gal.
> heated tank they drink out of. Now
> can they water founder on that?
> Been told to only give them 5 gal.
> each a day. What should I do??