The question of how long you can safely store water for emergencies is complex because water itself does not truly spoil. The potability of stored water is determined by the container and the environmental conditions, not the water’s inherent stability. Over time, chemical and biological factors can compromise the purity of the supply. Understanding these variables is necessary for establishing a dependable emergency supply.
The Shelf Life of Commercial Bottled Water
Commercially bottled water often displays an expiration or “best by” date, which can cause confusion about water’s longevity. This date generally does not reflect the water going bad, as the FDA does not mandate a shelf life for bottled water. The inclusion of a date became common after a 1987 New Jersey regulation required a two-year expiration period, a practice adopted widely by manufacturers.
The date primarily serves as a guideline for the integrity of the plastic bottle itself. Plastic materials, particularly polyethylene terephthalate (PET), can slowly degrade over time, resulting in the leaching of chemicals or microplastics into the water. Exposure to heat or direct sunlight significantly accelerates this degradation, potentially altering the water’s taste and quality. For unopened bottles stored under ideal cool and dark conditions, the recommended maximum storage time is typically one to two years.
Guidelines for Long-Term Emergency Water Storage
Storing tap water at home for emergency use requires specific preparation steps. The first step involves selecting the correct container, which must be food-grade plastic, such as High-Density Polyethylene (HDPE), or glass, to prevent chemical contamination. Containers should be opaque to block light, which inhibits the growth of algae and other microorganisms.
For short-term storage (generally considered six months), municipal tap water already treated with chlorine does not typically require additional treatment before sealing. For long-term storage, or for water sourced from untreated sources, purification is recommended prior to sealing. This involves adding unscented liquid household chlorine bleach (5% to 9% sodium hypochlorite). A common guideline is to add four to five drops of bleach per gallon of water to prevent microbial growth.
Factors That Determine Storage Longevity
Several environmental factors influence how long stored water remains safe and palatable. High heat accelerates the degradation of plastic containers, increasing the rate at which chemicals may leach into the water. Storing water in a cool environment, ideally between 50°F and 70°F, minimizes chemical transfer and inhibits microbial growth. Light exposure, particularly direct sunlight, promotes the growth of algae if the container is not completely opaque.
The container material itself affects longevity; while glass is chemically inert, food-grade HDPE plastic is preferred for its durability. Containers must be tightly sealed, and they should be stored away from volatile substances like gasoline or pesticides. Plastic can be permeable to these vapors, which can compromise the water’s taste.
Maintaining and Refreshing Stored Water
Active management is necessary to ensure the continued safety and quality of stored water. Water rotation is the most common maintenance practice, involving replacing the entire supply on a regular schedule. The general recommendation for home-stored tap water is to replace it every six months to one year. This rotation helps prevent microbial growth and maintains freshness.
When replacing the supply, the older water should be used for non-drinking purposes, such as cleaning, rather than being discarded. If water has been stored past the rotation schedule, it can be re-purified before consumption by re-treating it with chlorine bleach or boiling it for one minute. Signs that stored water may no longer be safe include cloudiness, discoloration, or a foul odor, at which point it should be safely discarded.