water consumption

I can find information on estimated water consumption for baby chicks and for adult chickens but nothing in between. Does such a "by age" chart exist?

I have five birds that are coming up on six weeks. When they were babies in the brooder they drank from a normal waterer with a pint jar on it. They would drink about 2/3 of it every day. At about 3 weeks I introduced a horizontal nipple waterer to them. For the last week they have been in their coop and run (having a fantastic time). They only have the nipple waterer now. It is a five gallon bucket with three nipples. i filled it about 3/4 full last week. I see them use it but the level hasn't changed all that much in a week. I was assuming i would have to fill it at least once a week if not more. They seem healthy and active. They are pooping and eating. Since switching to the nipples their poop is not nearly as wet (it was pretty runny before), but it still seems to have plenty of moisture.

I figure it would be obvious if they were dehydrated. So, I am just curious about what their water consumption should be at six weeks. What about two months? Three? Four? When does it level off?

Thanks