Are you going to need to refill your chicken waterer once a day... or once a week? You might be wanting to plan ahead for what size waterer you'll need for your new backyard flock. If you're thinking about this already, good for you! You'll be much happier if you've thought everything through and planned everything out, first. To choose the right waterer for you, it can be helpful to have a rough idea about how much your birds will drink.
That said, many things will affect how much your flock will drink: larger birds will drink more. Birds not laying will drink less. In the heat of summer, your birds will drink more, and so on. So, keeping in mind that you'll still need to check their waterer regularly--that is, don't just operate on a schedule--we can give you a rough estimate so you can plan things out.
In general, adult large fowl chickens will drink about a pint of water per day. That means that if you're using a small, 5 quart waterer, it will provide enough water for ten adult large fowl chickens for one day... or for one chicken for more than a week. Again, your flock will drink more, sometimes up to twice as much, if it's a very hot summer day, and they're laying. And tiny bantams--even on a hot day--are not likely to drink nearly as much. So do be sure to keep checking to make sure your birds have plenty to drink.
The other thing to think about when you're making your plans is to make sure you have enough space for the size waterer you're wanting. For instance, you don't want to purchase a 5 gallon waterer if it won't actually fit where you want it to go. Remember, you may sometimes choose to provide more than one waterer of a smaller size, if they'll fit better in your space.