According to the International Bottled Water Association, "Bottled water can be used indefinitely if stored properly." However, heat and time can adversely effect a bottled water's quality.
Though the United States Food and Drug Administration regulates the bottled water industry, it does not require companies to include expiration dates on bottled water. Many manufacturers include a two-year best-by date as a courtesy, but water may retain freshness well beyond its expiration date.
For best results, store glass and plastic water bottles in dry, dark places away from heat and light. Sunlight may encourage a plastic water bottle to leach chemicals called phthalates from its cap or lining into drinking water. Also keep bottled water far from household chemicals, detergents and paint thinners, as water may absorb a nearby chemical's taste or odor.
While a bottle's stamped expiration date generally confirms water's freshness, certain physical signs may still suggest spoilage. A bent or deformed bottle indicates its overexposure to sunlight, while a strange aroma or flavor denotes staleness. Occasionally, algae may form in bottled water.