Are Plastic Water Tanks Safe?
Yes, at room temperature, and the honest version has numbers in it. What leaches from plastic is driven by heat and time, which makes where you put the tank the whole decision.
Yes, with a condition that turns out to be the whole answer: keep it out of the heat.
The pages that rank for this question fall into two groups. One is alarmed and gives no quantities. The other sells plastic tanks. Neither gives you a number you can hold anything up against, and the numbers are public.
What actually comes out of the plastic
Two things get discussed, and they behave differently.
Antimony is a catalyst used in making PET, the plastic in single-use bottles. It migrates into the water slowly, and the rate roughly doubles for every 10°C of warming. EPA’s maximum contaminant level for antimony in drinking water is 0.006 mg/L, and the health effects it lists at exceedance are increased blood cholesterol and decreased blood sugar.
The number that gets quoted around this is from Consumer Reports, citing work in which antimony exceeded FDA limits within five days at 167°F. That is worth reading precisely. One hundred and sixty seven degrees is a closed car in direct sun. It is not a basement, a garage, or an attic in most of the country.
BPA is a different story, because water storage containers are HDPE, and HDPE does not contain BPA. The BPA conversation belongs to polycarbonate, which is what old five gallon office cooler jugs were made of. If your storage is the opaque blue or white rigid plastic that everything in this category is made of, BPA is not your question. Food grade and BPA free are separate claims and neither is the one that matters here.
| Where it sits | Rough temperature | What that does | What to do | Verdict |
|---|---|---|---|---|
| Basement or interior closet | 50 to 70°F | Leaching too slow to matter over years | Nothing. This is the answer | CDC's recommended range |
| Attached garage | 40 to 90°F | Seasonal swings, slow degradation of the plastic | Rotate on schedule and check the containers | Acceptable, with attention |
| Detached shed or uninsulated attic | Over 100°F in summer | Measurable leaching, plastic goes brittle | Move it, or treat it as non-potable | The real problem case |
| A closed car in the sun | Up to about 160°F | Antimony exceeded FDA limits within five days at 167°F | Not storage. Drink it or discard it | The only genuinely bad case |
Temperature is the entire variable
This is why the answer is a location and not a material.
Chemical migration into water follows temperature and time. At 50 to 70°F, which is the range CDC recommends for stored water, the process is slow enough that it does not accumulate to anything over a rotation cycle. At 100°F it is fast enough to notice. At 160°F it is fast enough to measure in days.
Heat also does something simpler and more consequential: it degrades the container itself. A jug that has been through three summers in an uninsulated shed goes brittle, and brittle containers split when you move them. In practice far more stored water is lost to a failed container than to anything that leached into it.
What to do about it
Put it somewhere cool and dark. This one decision resolves most of the question. An interior closet beats a garage, a garage beats a shed, and anything beats a vehicle.
If it has to live somewhere hot, demote it. Water stored in a hot shed is fine for flushing, washing and cleaning, which is most of what a household actually consumes water for during an outage. Keep the drinking supply inside and let the hot storage cover sanitation.
Rotate on the shorter interval when it is warm. The six month rule already assumes cool and dark. Somewhere warm, treat it as shorter and check the containers when you turn them over.
Do not solve it by buying different plastic. There is no household plastic that is meaningfully more heat-stable at this price point. Glass and stainless steel are the alternatives, and both cost more per gallon and weigh more.
The comparison nobody makes
Set this against the alternative, which is not having water.
The measured risk from properly stored plastic is a chemical exposure well below regulatory limits, over years, in a cool room. The risk on the other side is a household with no drinking water during an outage. Those are not the same order of magnitude, and a page that raises the first without naming the second is not helping anyone decide anything.
Store it in food grade plastic, keep it cool, rotate it on a schedule, and spend the worry somewhere it buys you more.