You've forked over money for a trip to Botswana, or Belize, or Bora Bora, and getting sick ranks high, maybe at the top, on the list of things you don't want to do. Amoebic dysentery, diarrheal diseases, and parasitic worms are associated with poor choice of water and food in many countries. Boiling kills organisms that make people sick. In fact, the time it takes water to reach the boiling point, even at high altitudes, kills organisms. So by the time water has reached the point of boiling, it is safe to drink.
Filters differ greatly in their ability to disinfect water.
Some filter out only protozoa, such as Giardia and Cryptosporidium. Some filter out protozoa and bacteria. Be sure you know the type and effectiveness of a filter a client is depending on. Chemicals can be added to water to kill harmful organisms. Iodine and chlorine are safest and most effective, but no chemical guarantees water safe from Cryptosporidium.