Yes, old water in a bottle, especially a reusable one left unwashed or a single-use plastic bottle left in heat, can make you sick by harboring bacteria, mold, or leaching chemicals, potentially causing gastrointestinal issues or allergic reactions, though properly stored bottled water is generally safe until its expiration date. The biggest risks come from contamination in reusable bottles (mouth contact, moisture) or heat exposure degrading plastic, so regular cleaning and avoiding hot cars are key.
The longer water sits, especially in the wrong conditions, the more likely it is to have an off taste, possible chemicals, or even bacteria growing. That doesn't mean you'll automatically get sick from one sip, but over time, it's not worth the risk. To ensure your drinking water is safe, always inspect the container.
If you do get sick, how you feel depends on the type of infection. For many waterborne infections, you start feeling sick 2 to 10 days after drinking infected water. You might have diarrhea, stomach cramps, nausea, vomiting, a fever, or foul-smelling gas or feces.
Unopened bottled water can technically last forever (but at least two years) if stored correctly. Once opened, it lasts a couple of days. Water in reusable bottles can last a couple of days before, in my experience, it starts to taste a little stale.
Drinking moldy water can certainly lead to symptoms like a runny nose, itchy throat, and dizziness, as mold exposure can trigger reactions similar to those of allergies or mild food poisoning. Mold in water, especially if consumed over time, can cause these irritations in sensitive areas like the throat and nose.
What are symptoms and effects of mold exposure?
A: If you find yourself drinking moldy water, the most important thing to do is to seek medical attention immediately. Mold contains many potentially harmful toxins and spores that can cause serious health problems if ingested.
Signs of Spoiled Bottled Water
Spoiled water has a distinctly off-putting odor and taste. There could be a stale or musty flavor. Be sure to avoid drinking water that has a moldy, foul, or chemical-like odor. The appearance may be off as well.
Bacteria thrive in moist environments. Water bottles, by their very nature, are constantly exposed to moisture, making them susceptible to bacterial contamination. While many bacteria prefer moderate temperatures, many can still grow at room temperature.
Add warmth, lack of cleaning, and tight lids, and within a few days, your bottle can turn into a breeding ground. In one week, the risk of contamination is high. By two to three weeks, both bacterial build-up and plastic leaching in disposable bottles make the water unsafe for drinking.
Drinking contaminated, or unclean, water can make you sick with diarrhea, vomiting, and stomach pain.
Monitor for Symptoms
Keep a close watch on your body for any symptoms that may arise after drinking contaminated water. Common symptoms include diarrhea, nausea, vomiting, and abdominal pain. If you notice any of these signs, contact a healthcare professional immediately.
Common Symptoms: Be vigilant for symptoms associated with contaminated water, including gastrointestinal issues (diarrhea, stomach cramps), nausea, vomiting, respiratory problems, skin irritation, fatigue, or any unusual health symptoms.
Dirty water bottle symptoms
Symptoms of having water bottle bacteria or dealing with mold in your water bottle could include: Sore throat. Runny or stuffy nose. Congestion.
“Everything that touches our reusable water bottles can transmit bacteria. We put our mouth to the water bottle, we lift the straw, we set it down – so bacteria can be transferred from any contact that's made,” explained Marianne Sumego, MD, a primary care physician with Cleveland Clinic.
7 Signs Your Tap Water Might Be Contaminated
Individuals who are sensitive to mold may experience allergy flare-ups and respiratory problems based on the mold growing inside their water bottles, underneath the caps, inside the straws and even on the rubber ring that goes around the bottom of many stainless-steel models.
Worldwide, production sites have similar problems with this type of bacteria within the bottle filling process [[23], [24], [25], [26]]. According to the Codex Alimentarius Austriacus, faecal indicator bacteria such as E. coli and other coliform bacteria should not be detectable in 250 mL of bottled water [27].
Bacteria on an unwashed reusable water bottle multiplied more than 600,000x in just one month. From only 50 CFUs on day one to over 30 million CFUs after 30 days. Bacteria also multiplied dramatically in one week, reaching 5.5 million CFUs, a 110,000x increase from day one.
Water is a natural substance and does not go bad, however the plastic water bottle will degrade over time and begin to leach chemicals into the water, which is why it is always important to choose BPA free bottled water. ✅ How long can you keep bottled water? The recommended shelf life is two years.
Final Thoughts. Bottled water doesn't technically expire, but its taste and quality can change over time depending on storage conditions. Properly stored bottled water remains safe to drink beyond its best-by date, but heat and prolonged exposure to plastic can affect its freshness.
Water itself does not expire, but the containers it is stored in and the conditions of storage affect its safety. While tap water can remain safe for up to six months if stored properly, opened bottled water—especially in plastic—can develop bacterial growth, mould, and chemical leaching within days.
“Having shortness of breath or trouble breathing, nausea, vomiting and diarrhea within a day or so of eating moldy food could be a sign of food poisoning or an allergic reaction,” Spina said. Symptoms of mold exposure are not usually an emergency, but in some instances, you should seek immediate attention.
Whether you're staring at a visible colony or you suspect there's a problem, mold in a water bottle should be treated by simply throwing out the container and purchasing a new one.