When can toddler go in a normal temperature swimming pool?

I have been taking my son to swimming lessons at a specialist children's swimming pool (Swim!) since he was quite small and he loves it. The pool there is heated to 31 degrees so it's warmer than a standard pool, which I think are around 29 degrees.

He's now 1 and loves swimming. When did you take your children to a normal pool at a leisure centre rather than a heated pool without them wearing a warmer?