Does Distilled Water Expire? The Quick Answer
Sealed distilled water does not expire, but it does not stay perfectly pure forever either. The FDA does not require expiration dates on bottled water, including distilled water. Manufacturers print "best by" dates -- typically 1-2 years from production -- primarily because plastic containers can leach trace amounts of chemicals into the water over extended periods, and the water may absorb odors from its storage environment.
Once you open the container, the clock starts ticking. Exposure to air introduces carbon dioxide (which lowers pH to around 5.8), airborne bacteria, dust particles, and other environmental contaminants. For this reason, the shelf life of opened distilled water depends heavily on how you store it and what you plan to use it for.
If you are using distilled water for baby formula preparation or drinking, opened containers should be used within 1-2 weeks. For CPAP machines and humidifiers, opened distilled water remains suitable for 1-2 months when stored properly. For automotive and appliance use like steam irons and car batteries, properly sealed opened containers last 6-12 months.
How Long Does Distilled Water Last?
The shelf life varies significantly based on whether the container is sealed or opened, and the intended use.
Sealed (Unopened):
- Commercial plastic bottles: 1-2 years (manufacturer recommendation), safe indefinitely
- Glass containers: Indefinite with no quality degradation
- Home-distilled in glass: 1-2 years (use sterile filling practices)
Opened:
- Drinking and baby formula: 1-2 weeks (2-3 weeks refrigerated)
- CPAP machines: 1-2 months
- Humidifiers: 1-2 months
- Steam irons and appliances: 6-12 months
- Car batteries and cooling systems: 1-2 years
The difference between sealed and opened shelf life comes down to contamination exposure. Sealed containers maintain the near-sterile conditions achieved during the distillation process. Once the seal breaks, every exposure to air, hands, or pouring surfaces introduces potential contaminants.
Signs Your Distilled Water Has Gone Bad
Distilled water that has been contaminated shows recognizable warning signs. Inspect your water before using it, especially for medical or infant applications.
Visual indicators:
- Cloudiness or haziness where the water was previously crystal clear
- Floating particles, specks, or sediment at the bottom
- Green, brown, or yellowish tint indicating algae or bacterial growth
- Film or sheen on the water surface suggesting biofilm formation
- White mineral deposits on the container (indicates the container was previously used for tap water)
Smell and taste:
- Any odor at all -- properly stored distilled water is completely odorless
- Musty or earthy smell suggesting mold or bacterial contamination
- Plastic or chemical taste from container degradation
- Stale or flat taste beyond what is normal for distilled water
Container warning signs:
- Swelling or bulging of plastic containers (gas production from bacteria)
- Cracks, damage, or discoloration of the container
- Loose or damaged seal
- Container stored near chemicals, gasoline, or solvents
If any of these signs are present, discard the water immediately. Do not attempt to re-distill or filter contaminated water for medical or infant use -- start with a fresh batch or new sealed container.
Best Storage Practices for Distilled Water
Proper storage maximizes shelf life and prevents contamination. The CDC guidelines on household water storage provide the foundation for these recommendations.
Container selection:
- Best choice: Glass containers. Mason jars, glass bottles, or borosilicate laboratory bottles are inert, do not leach chemicals, and allow easy visual inspection. Clean with hot soapy water and rinse with a small amount of distilled water before filling.
- Good choice: Food-grade plastic. HDPE (#2 recycle symbol) or polypropylene (#5) containers minimize chemical leaching. These are the same plastics used in commercial distilled water bottles.
- Avoid: Non-food-grade plastic, old milk jugs (residual proteins harbor bacteria), containers previously used for chemicals, and low-quality thin plastic that degrades quickly.
Storage conditions:
- Temperature: 50-70 degrees F in a cool, stable environment. Avoid temperature fluctuations that cause condensation inside the container.
- Light: Store in a dark location. Sunlight promotes algae growth even in distilled water and accelerates plastic degradation.
- Proximity: Keep away from chemicals, pesticides, gasoline, paint, and cleaning solvents. Vapors from these substances can permeate plastic containers over time.
- Position: Store upright with caps tightly sealed. Minimize the air space in the container by using appropriately sized containers.
Handling practices:
- Never pour distilled water back into the storage container after pouring it out
- Use clean utensils or pour directly rather than dipping hands or objects into the container
- Close the container immediately after each use
- Label containers with the distillation or opening date
Distilled Water Shelf Life for Specific Uses
Different applications have different purity requirements, which affects how long opened distilled water remains suitable.
CPAP machines: Use opened distilled water within 30 days. CPAP humidifier chambers operate at warm temperatures that can promote bacterial growth if the water is already partially contaminated. Empty and clean the chamber daily, and refill with fresh distilled water from your storage container. Never refill with water that has been sitting in the chamber overnight.
Humidifiers: Similar to CPAP machines, use opened distilled water within 1-2 months. Change the water in the humidifier tank daily rather than topping off old water. Mineral-free distilled water prevents the white dust problem and reduces bacterial growth compared to tap water, but it is not immune to contamination once opened.
Baby formula: The most conservative shelf life applies here. Use opened distilled water within 1 week, or 2 weeks if refrigerated. For infant applications, the AAP and FDA recommend extra caution with water quality. If in doubt about the age or storage conditions of your distilled water, open a new sealed container.
Car batteries and cooling systems: Opened distilled water stored in a sealed container remains suitable for 1-2 years for automotive applications. The purity requirements for batteries and radiators are less strict than for drinking or medical use, but mineral contamination from dirty containers can still cause corrosion.
Home brewing and aquariums: Use opened distilled water within 1-3 months. These applications benefit from distilled water's consistency but are less sensitive to trace bacterial contamination than medical or infant uses.
If you regularly use distilled water and want a reliable supply, consider making distilled water at home with a countertop distiller for about $0.25-0.35 per gallon rather than stockpiling store-bought bottles.
When to Discard Distilled Water
Follow these guidelines to determine whether your distilled water is still safe to use:
Discard immediately if:
- Any visible contamination signs (cloudiness, particles, color, film)
- Any unusual odor
- Container has been open for longer than the recommended shelf life for your intended use
- Container was stored in direct sunlight or near chemicals
- Container was previously used for non-food substances
Safe to use if:
- Sealed container within manufacturer date, stored properly
- Opened container within recommended timeframe, properly stored
- No visible or olfactory contamination signs
- Container is food-grade glass or approved plastic
For applications where water quality is critical -- CPAP machines, baby formula, nasal irrigation -- err on the side of caution. A fresh gallon of distilled water costs $1.00-1.50 from most grocery stores, making replacement far cheaper than the health risks of using contaminated water.
Check your local tap water quality to understand what contaminants distillation is protecting you from, and explore our guide on whether distilled water is safe to drink for the full health picture. You can also compare distilled vs purified water to determine which type best suits your needs, or explore reverse osmosis filtration as an alternative to distillation.