eeheeEnough to take it swimming in your swimming pool, shower, and wash your hands. I've taken it jet skiing and jumped off with it on and didn't have any water issues.
eeheeAccording to Pebble Support (http://help.getpebble.com/customer/portal/articles/1850071-water-resistance) it's good up to 5 atm or 50 meters, so you can do light water sports (swimming, snorkeling, paddling), but no diving and they say not to push buttons while under water. This was my main concern too as I do a lot of snorkeling.