While the water molecule itself does not inherently “go bad,” its potability, or safety for drinking, can be significantly compromised by external factors over time. Unlike perishable foods, water does not spoil in the same way, but its quality can deteriorate due to environmental influences and storage container characteristics. Pure H₂O remains stable, yet impurities and physical changes can render it undesirable or even unsafe to consume.
Understanding Water Quality Changes
Several factors contribute to the degradation of water quality in storage. Airborne particles, dust, and microorganisms like bacteria, algae, and fungi can enter water, especially if containers are not sealed. These biological contaminants thrive in stagnant water, leading to health concerns.
Chemical leaching from containers presents another concern, particularly with plastic bottles. When exposed to heat or sunlight, plastics such as polyethylene terephthalate (PET) can release trace chemicals like antimony, bisphenol A (BPA), and microplastics into the water. Dissolved gases also affect water quality; carbon dioxide from the air can dissolve into water, altering its pH and leading to a stale taste. For tap water, chlorine, which acts as a disinfectant, gradually dissipates when exposed to air. This loss of disinfectant properties makes the water more susceptible to microbial growth, affecting its taste and safety.
How Long Water Remains Potable
The length of time water remains potable varies significantly depending on its source and how it is stored. Unopened commercially bottled water often carries a “best by” date, which typically refers to the degradation of the plastic bottle rather than the water itself. If stored under optimal conditions, unopened bottled water can remain safe to drink for years, though its taste may change.
Once opened, bottled water becomes susceptible to airborne contaminants and microorganisms. Consume opened bottled water within four to six days if refrigerated, or much sooner if left at room temperature. Drinking directly from the bottle can introduce bacteria from saliva, further accelerating contamination.
Tap water stored in clean, sealed containers can remain safe for up to six months, though chlorine dissipation means it loses its protective barrier against bacterial growth. Water left in an open glass or container is exposed to dust and airborne particles, and is best consumed within hours or a day. Distilled water, being very pure, can last indefinitely in a sealed, non-reactive container. Once opened, its purity can be compromised, and it is best used within a few days to a week for drinking, or up to four weeks for general household use.
Recognizing Signs of Compromised Water
Identifying compromised water involves observing changes in its sensory characteristics. Visually, safe drinking water should be clear and free of particles. Signs of degradation include cloudiness, floating particles, or discoloration such as green, brown, or yellow hues, which can indicate algae, rust, or other contaminants. An oily film on the surface also indicates potential issues.
Unusual odors provide a strong indication of water quality problems. A musty, sulfuric (like rotten eggs), or chemical smell suggests contamination. Taste cues also signal compromised water. A stale, metallic, bitter, or otherwise unpleasant taste, or a salty or soapy flavor, indicates the water is no longer suitable for consumption. Some contaminants are not detectable by sight, smell, or taste, emphasizing the importance of proper storage practices.
Best Practices for Water Storage
Proper water storage is important for maintaining its safety and quality over time. Selecting appropriate containers is a primary step; food-grade, opaque, and airtight containers made of glass, stainless steel, or specific plastics like high-density polyethylene (HDPE) are suitable. Containers that previously held non-food items should not be used, as they may leach harmful residues into the water.
The storage location significantly impacts water quality. Water should be kept in a cool, dark place, away from direct sunlight, chemicals, and extreme temperatures, which can accelerate degradation and microbial growth. Containers should also be cleaned and sanitized thoroughly before filling, typically with soap and water followed by a mild bleach solution, and then rinsed completely. For long-term emergency supplies, implementing a rotation system is beneficial; stored tap water should be replaced every six months to ensure freshness and potability. For emergency preparedness, store at least one gallon of water per person per day for a minimum of three days, with a two-week supply being more robust.