With the water potentially contaminated in Bangkok, another basic skill worth remembering from my days on the farm: Using 'Potassium Permanganate' to clean and disinfect vegetables, salad leaves and fruit. (See the video below).
Potassium Permanganate is a purple crystal. You buy it in little bottles from pharmacies, drop a few crystals into water, which turns a deep purple, and then a quick soak of fresh salad greens like lettuce in the water (for 15 minutes) it kills the bugs and bacteria on the surface. Shake off the liquid and they are ready to eat.