Whether you are raising goats as part of a sustainable lifestyle or because you like to keep them as pets, they need a consistent supply of fresh, clean water to grow properly, stay healthy, and do their best in milk production. Pregnant and lactating does have the highest water needs, and when the weather is hot and dry, all goats need more water. A general rule is to give a goat between a half-gallon to four gallons each day per goat.
You can get by without a nearby water supply, but if your barn is any distance from your house, you'll find that hauling water and equipment back and forth is a lot of work. Plan ahead, even if it means digging a water line when you put in a new goat shelter or barn.
Even better is a sink and faucet with hot water. You can wash feed bowls and buckets without schlepping them to the house. And with dairy goats and the equipment they require, it's even more useful.
At a bare minimum you need a hose that reaches the barn or area where the goats hang out. Even with just that, if you don't want to be at the beck and call of your goats or if you actually have to leave the farm once in a while, you can use a stock tank and buy a float valve to attach to the hose. When the water is low, the valve opens to allow enough water through to refill the tank. Rubbermaid makes an inexpensive one that livestock supply stores carry.
Some people are fortunate enough to have a creek or a pond that goats can use for a water supply. Both are convenient but have the disadvantage of being more liable to become contaminated from urine, feces, and debris or from becoming stagnant. If you plan to use either of these sources, get the water tested first to determine whether it's safe for drinking. If you're on a city water source, talk to your water supplier about how to do this. If you have well water, you're responsible for its safety and can contact your local health department for information on getting it tested.