well my daughter is almost 3, and I still dont leave her in the tub on her own. I am a worry wart of a mother though if there are no towels in the bathroom I will either get her out or pull the plug and tell her to wait while I fetch one, or I get my hubby to grab one from the linen closet, so I dont have to take my eyes off her for a second. If I could wrap her up in bubble wrap I would! haha. Water really worries me cause u hear of so many stories about little ones drowning, a family members friend had their toddler drown in a horse troff and he was only 2, its so sad you can never be too careful.

But at a guestamate I would say 5 and up? I dont know though as this one is my 1st toddler, I am not sure when I will feel comfortable myself leavin her in the tub on her own, but it does happen one day I guess, They all grow up, too too quickly!