If you have city water? If so, it’s most likely treated and unlikely to grow anything. If you, like us, are using well water, then it’s not treated with the mild toxins (chloramine, etc.) that you get in city water. Obviously countless humans and other creatures drink city water without known ill effects, but if you do chose to add chlorine (which will gas off unlike chloramines often used in municipal treatments), it’s very important to add the correct amount.
If your un-soiled, covered well water begins to stink after a day or two, you may want to have it tested to make sure it’s safe. If it’s covered and the vessel is clean, it should last several days at reasonable temperatures.
Nipple waterers do help, but it’s vital that your birds know how to use them before you leave them alone. Also if it’s very hot, it can be difficult for the birds to hydrate themselves sufficiently via nipple waterers, especially meat birds, whose metabolism requires large amounts of water.
Cup waterers are easier to learn, especially if you get the ones operated by a float valve. IME, the birds will soil the cup, fill it with bedding, etc. if there’s anything available to fill it with. You may have better luck. I’ve only tried mine in brooder so far. I may add them to a bucket and hang it over grass in my tractors. I think that would work better.