I want to pour a concrete basin for a bird bath. First I thought to use hydraulic cement so it is waterproof. But this stuff sets really fast and seems to be only for patching. So I bought a concrete sealer from Home depot: Silkagard ProSelect Natural Look Clear Sealer. Is it safe to use for drinking water or will it outgas or release otherwise some toxic substances? I don't want to harm the birds.
If you're worried about the toxicity of the sealer, there are numerous options that are food-grade (for humans, no clue about how that applies to birds). These are primarily used for sealing poured concrete counter-tops. A quick Google search should turn up some options, or you can just ask at your local big-box for a food-grade concrete counter-top sealer.