A.O.
My opinion is nothing if you are in the water with him and can give him your undivided attention. Teach him how to go under the water, hold his breath, blow bubbles etc... My son was 2 and going off the diving board and swimming back to the side, unassisted and without floaties. Kiddos need to learn to swim as young as possible. This is not to say that you don't still need to be extremely cautious!!! But if a child falls in the pool they need to know how to get back to the side to hold on until help arrives.