Here's when you need get rid of your plastic water bottle

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I have this one plastic water bottle I take to the gym, and I don't want to buy another one because a) the environment and b) I'm cheap.

I've been using it for a few weeks now, and I wondered: Is that safe?

Plastic water bottles are made from polyethylene terephthalate, or PET. The US Food and Drug Administration has approved PET for single and repeated use, so that's a good sign.

But manufacturers make these plastic bottles for the purpose of a single use, so they don't last forever.

Two things can happen as you reuse plastic bottles over and over: They can leach chemicals, and bacteria can grow in them.

It turns out chemical leaching happens in such small amounts that we don't have to worry about that.

Researchers from Arizona State University collected nine different brands of bottled water and measured how much of a particular chemical, antimony, the bottles released.

Antimony is commonly found in the plastic used to make water bottles. If ingested, it can cause vomiting and diarrhea, but it's not considered a carcinogen. The US Environmental Protection Agency has set the maximum concentration for antimony in drinking water at 6 parts per billion (ppb).

The researchers found the water in the plastic bottles had only 0.195 ppb at the beginning of the study and 0.226 ppb three whole months later — way below the EPA limit. (They also tested the local tap water for comparison and found antimony levels of 0.146 ppb.)

The study can't say how much antimony might leach into the water after more than three months, but the results suggest that — with reasonable water bottle use — the levels in your water will remain well within what's considered safe.

There have been reports of DEHA, a possible carcinogen, leaching into bottled water, too, but the Natural Resources Defense Council says this is an "urban legend."

So we don't have to worry about leaching.

Bacterial growth, however, is a problem if you're reusing a plastic a water bottle again and again.

The PET Resin Association, a plastics industry group, recommends washing water bottles after each use with soap and hot water, and thoroughly drying them, to get rid of the bacteria. They say consumers shouldn't reuse bottles if they have scratches inside, since bacteria can get stuck in there.

I haven't been washing that gym water bottle, and I doubt I'll go through the trouble of hand washing it. It's nice to know that I can reuse it, but I'll probably recycle this one and start using a dishwasher-safe permanent water bottle instead.

So you should recycle your plastic water bottle if it has scratches or if you haven't washed it.

Experts, writing in the journal Practical Gastroenterology, say that recycling that bottle is the safest option, but that it's okay to keep using it — as long as you keep it clean.