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The average person needs 1 gallon (4 liters) of water each day, half for drinking and half for food preparation and hygiene. Increase this number to 1.5 gallons (5.5 L) per person or more for children, nursing mothers, and sick people, and for anyone in a hot or high-altitude climate. Based on these numbers, try to store a 2 week supply for your household. In case of an emergency evacuation, store a 3 day supply in easily transportable containers. For example, 2 healthy adults and 1 child need (1 gallon or 3.8 liters / adult) x (2 adults) + (1.5 gal or 5.7 liters / child) x (1 child) = 3.5 gallons (13.25 liters) per day. A 2 week supply of water for this household is (3.5 gallons or 13.25 liters/ day) x (14 days) = 49 gallons (185.5 liters). A 3 day supply would be (3.5 gallons or 13.25 liters/day) x (3 days) = 10.5 gallons (40 liters). In areas that regulate bottled water, including the U.S. and E.U., sealed bottles of water are already sanitary and will stay good indefinitely. If you go this route, you do not need to worry about selecting appropriate containers or purifying the water. Check the label for certification by the IBWA (International Bottled Water Association), NSF (National Sanitation Foundation), or UL (Underwriters Laboratories). These demonstrate the product has met safety and quality standards. This is more important in countries that do not regulate bottled water. Look for the resin identification code on plastic containers, which typically consists of a number printed next to the recycling symbol. Avoid containers marked “3” (for polyvinyl chloride, or PVC), “6” (for polystyrene, or PS), and “7” (for polycarbonate). These materials can be hazardous to your health. Wash them with soap and hot water, then rinse. If a container previously held food or drink, disinfect it with one of the following methods:  Fill with water and mix in 1 tsp (5 mL) liquid household bleach for every quart (approximately 1 liter) of water. Swish to touch all surfaces, then rinse well.  For stainless steel or heat-safe glass, submerge in boiling water for 10 minutes, plus 1 minute for each 1,000 ft (300 m) of elevation above an altitude of 1,000 ft (300 m). This is the best method for steel, since chlorine bleach can corrode the metal. . If your tap water is not safe to drink or if you get your water from a well, disinfect it right before storage. The best way to do this is to bring the water to a rolling boil for 1 minute, or 3 minutes at elevations above 5,000 ft (1,000 m).  If you cannot boil the water, or do not want to lose water by boiling it, bleach is the next best option:  Mix in ½ tsp (2.5 mL) of unscented, additive-free bleach for every 5 gallons (19 liters) of water. Double the amount of bleach if the water is cloudy or discolored. Let the water sit for half an hour. If you cannot smell a faint chlorine scent, repeat treatment and let sit another 15 minutes. In an emergency, you can also disinfect small amounts of water with water purification tablets. However, use these sparingly, as excessive use can impair thyroid function. Boiling or chlorine will kill microorganisms, but they will not remove lead or heavy metals. If your water is contaminated by runoff from farms, mines, or factories, pour it through an activated carbon filter and a reverse osmosis (RO) filter. You can make your own filter out of common materials. While not as effective as a commercial filter, it will remove sediment and some toxins.
Decide how much water to store. Consider bottled water. Avoid containers made from hazardous plastics. Clean the containers thoroughly. Disinfect water from unsafe sources Filter out contaminants.