If the leak is on the top of your water-bed mattress, you do not have to drain the bed. Leaks on the edges of the mattress may require partial draining, while leaks on the bottom of the mattress require complete draining of the water bed. Seam rips are not patchable and are considered manufacturer defects; contact the water-bed manufacturer regarding replacement.
Water-bed patch kits come with a vinyl patch and vinyl-safe glue. These are the appropriate materials for patching your mattress. Do not attempt to use rubber cement, high-intensity glue or any other adhesive to patch your water-bed mattress.
Locate the puncture and circle it with a permanent marker. If you have trouble finding the hole, follow the water and rub dish soap onto the area where you think the leak is located. Push on the mattress to force water through the hole and watch the area for bubbles. Dry the mattress. Cut a patch into a circle slightly larger than the puncture and apply a small amount of adhesive to the hole and the back of the patch. Press the patch onto the hole and allow it to dry before putting weight on the bed.
Cover your mattress with water-bed sheets; they have deeper pockets and are designed to reach all the way down around the bottom edge of the mattress. Keep the bed made when you aren't sleeping in it. Try to discourage pets from walking on the bed, especially during bedding changes or any time the mattress vinyl is exposed. Don't allow debris to get between the mattress and the frame.