It's so important to ensure that your backyard birds have plenty of fresh clean drinking water during the summer months. We change our birdbath water twice per day because the birds use the baths quite a lot for bathing and drinking. The warmer the weather the more use the birdbaths will receive.
In fact, we scrub the birdbaths with a water/bleach solution which cleans them while reducing the growth of green slime that begins to build up after about two weeks. Having clean birdbaths in your yard will attract birds from all around and watching them splash around in the bath is so much fun adding to the joy of birdwatching.