My mother always uses water that is around (or at) room temperature when she is baking something with yeast. In fact, her advice in regard to baking is : ALWAYS use ingredients at room temperature. The only exception being butter for short crust or flaky pastry. Use that as cold as possible. Her advice for short crust and flaky pastry is: If you don't feel entirely confident, chill all your ingredients. Even the flour. This way you are sure everything stays cool longer. If the weather is chilly or very humid, Mum has a trick to 'dry out' the flour she uses for bread and warm it up a little: zap it in the microwave for a couple of seconds (30 at most), then whisk thoroughly. This will cool down the flour a little, test it with your finger to make sure it doesn't actually feel hot or it will kill the yeast. If it's too hot, whisk a bit more. If it feels more or less the same temp as your finger when you push it in the flour, you know you should be fine. This slight heating will help the yeast along and is safer than using tepid water.