Currently purification tablets are hard to come by in 3.0. As the PvE in 4.0 is to be heavily emphasized, there should be other ways to boil water.
Here are a few suggestions that I came up with.
This simple method removes bacterial and viral contaminants, but not chemical contamination. Only suitable for water such as those found in rivers, streams, and ponds.
Evaporates the water and then condenses the vapor in a seperate container. Suitable for all types of fire, but requires a still and a heat source in order to work.
Found in 2% tincture bottles at pharmacies. Requires five drops per liter, but takes 30 minutes in order to work. Also, it loses potency at temperatures below 68 degrees Fahrenheit (21 degrees Celsius). Like boiling, it does not work on chemical contaminants.
Purification Tablets (chlorine, not iodine)
One tablet per liter. The most space efficient method. Does not work on chemical contaminants.
Works similarly to iodine, requires three drops per liter, but works in all temperatures. However, the bottle is significantly larger and more bulky. Ineffective against chemical contaminants.
By leaving dirty water out in the sun for three full days, all microbial life can be effectively killed. However, the bottles must be clear and the sky clear. Does not work on chemical contaminants.