It all depends on how quickly you want your water to be purified. If you are very impatient and are looking for a quicker way to get around the process, you could use warm water. Indeed, the tablets are going to dissolve faster in such water.
Worth noting, however, is you should not do so in hot water. Ensure that the water you are using is nothing warmer than lukewarm. Of course, remember, waiting an extra 10 minutes to kill off as many micro-organisms as possible will be worth it.