You should join up to a mother and baby or toddler group.
Me and My son go and he is 3 we have been going for a year now - but he did go into the water a few other times before he was 3.
He loves it he can swim with a float and armbands he is getting pretty good at it now

start them young
The only thing I have heard is that you shouldn't take them swimming until they have had the jabs - so not before 4 months - which is fair enough.