A.Tile consultant Michael Byrne responds: So-called "non-slip" coatings, which work by etching the surface of the tiles, are available. Use of non-slip coatings, however, can affect the color, hue, and light-reflecting qualities of the tiles.

How you respond to this client may depend on who specified the tiles. If the tiles have a polished surface, they may not be appropriate for the intended use. If you have no responsibility regarding the selection or purchase of the tiles, you should direct your customer to a contractor who is trained in the application of non-slip coatings, which is a specialty trade. (I don’t recommend that you attempt to install a non-slip coating, since the work has resulted in some rather protracted lawsuits.)

Although most people expect a bathroom floor to get wet, a residential kitchen should not be expected to have water on it. If water is spilled on any kind of flooring, it should be removed promptly, and foot traffic should be restricted until the area is dry. Since a film of cooking grease or oil, with or without water, can be slippery, kitchen floors should be cleaned on a regular basis. If the owners expected to have water on their floor, they should have made that clear at the time the tile was being specified, so that a special tile could have been used.