Because of the name of this thread, there's one warning I feel compelled to throw in here: Neither of these tablets 'purify' water, they only 'disinfect' it to some degree.

It's important to remember that water contains runoff from the surrounding land. If there are crops, there are agricultural chemicals in the water. The same holds true if there are manufacturing or mining sites upstream.

Bringing water to a boil will kill everything that either of these tablets will kill.

To remove other impurities, you will need a filter.