Concerned about Viruses?
It is very rare for Water borne viruses to be present in drinking water. The only three of concern that may occur are Polio, Hepatitis and Norovirus. The only way that they can get into the water system is from the excrement of an infected person. Therefore, untreated raw sewage must be present. Even in underdeveloped countries this is rare. (but it can happen particularly during floods).
Polio is the most rare, and most westerners are already vaccinated. Are you?
Hepatitis, is not so rare, however, its common form of transmission is through direct human contact, (handshaking, sneezing, etc). Poor hygiene (antibacterial hand washing is key) is the main source.
Norovirus is very common, but is normally found in salt water coastal areas where there are sewage outlets. Again, its main source of transmission is similar to Hepatitis, plus swimming. Remember David Walliams swimming in the tidal area of the River Thames a couple of years ago? That was norovirus!
Your best protection against viruses when travelling is to check the world health organisation website before you leave http://www.who.int/countries/en/
If there has been an outbreak, be vigilant. Take antibacterial hand wipes. When showering/bathing, don’t allow any water into your mouth. Wash your mouth / nose with your wipes immediately upon exiting the water. Don’t take ice in your drinks, and avoid salads. Remember, Only start to panic like this if there has been an outbreak announced.