What to do if inflatable boat gets accidentally punctured on the water?

First of all - do not panic. Most inflatable boats, rafts and kayaks have several air chambers, and if one of chambers gets punctured, the boat will stay afloat due to the buoyancy of the remaining air chambers. 

Inflatable air chambers are separated by internal baffles that keep chambers separate in case of accidental puncture, and designed to equalize air pressure between all interconnected chambers.

We suggest that you always carry on board the following items - Personal Flotation Device (PFD) for each passenger along with a whistle, a marine emergency radio to call the Coast Guard for help if necessary, a hand pump, piece of duct tape (Gorilla Tape) and a small bottle of acetone.

If boat gets punctured below the water line, there is nothing much you can do except for pumping air with a hand pump in order to slow down the air leak.  Punctures in accessible places, inside the boat, can be temporarily fixed with a piece of duct or Gorilla tape. To insure a good seal, the area around the puncture should be cleaned with acetone before applying duct tape. After that, you can pump in air to slow down the escaping air, and get ashore as soon as possible.