Bottled water is generally safe – check that the seal is intact at purchase. Tap water in Ulaanbaatar and other cities is considered bacteria-free, however antiquated plumbing means the water may contain traces of metals that won’t be good for your long-term health. Be cautious about drinking from streams and lakes, as they are easily polluted by livestock. Water is usually OK if you can get it high up in the mountains, near the source. If in doubt, boil your water. The best chemical purifier is iodine, although it should not be used by pregnant women or those with thyroid problems. Water filters should filter out viruses. Ensure your filter has a chemical barrier such as iodine and a small pore size (less than four microns).