The short answer is 11 inches.  If the water depth is above 11 inches, the chair will start to float and become unsteady.  The good news is that our Costarondack looks just as fantastic around your pool as it does in your pool! If you have any questions about placing our Costarondack in your pool, please give us a call 830-249-8947 or send an email to info@baskoutside.com and we will be happy to help.