Puddles that fill up when it rains.

When it rains, new water sources appear. Relief for the thirsty.

Maybe the rest of the time they are just dry. Or maybe even when they are dry they are hazardous pits of mud to get stuck in. Deceptive dry-appearing crust, large-enough dinos can break through and trying to get out drains stamina! Free food for carnivores! I'm getting carried away. Anyways, fresh water sources when it rains.