Is it safe to drink water from plastic bottles?

Probably. But it depends on the type of plastic the bottle is made from.

When it comes to a healthy drink, nothing can compete with water.

And in an effort to be more healthy, many of us make a point of carrying water bottles with us everywhere we go. But are our water bottles a health issue? Especially those made from plastic?

Generally, they are safe, but it depends on the kind of plastic the bottle is made of.

Most plastics are made of long chains of hydrocarbon molecules, built from simpler building blocks called monomers. Some plastics then have chemicals added to give them a characteristic such as flexibility or colour.

Buying bottled water

The 'single use' water bottles that you typically buy at milk bars, service stations and the like are usually made from polyethylene terephthalate (abbreviated to PET or PETE), an inexpensive and lightweight plastic. Its recycling code (the number in the centre of the triangle of arrows found on most plastics) is 1.

"PET is not one of the plastics that one would think has a propensity to cause a problem," 

Agrees with the US FDA, which says that PET bottles are safe for use and reuse so long as they are washed properly with detergent and water to remove bacteria.

The safety of using PET bottles was questioned after a student research project hit the headlines. The 2001 study found traces of a phthalate — a potentially harmful 'plasticiser' used to make some plastics more flexible — in water from PET bottles, but the research hadn't been verified.

PET has never contained phthalates and the public's association between the two could be based on the plastic's name.

And while some preliminary studies have suggested water from PET bottles can contain as-yet-unidentified substances with 'oestrogenic' properties (which disrupt the body's normal hormone regulation),  no rigorous scientific review has backed these.

A substance called antimony is used in PET production and it can leach into the water in PET bottles. However, this doesn't pose much of a risk.

"Antimony is not in the same league as lead or mercury toxicologically so the likelihood of harm is low,'.

Using your own bottle

But what if you've decided not to buy bottled water, but to use a refillable water bottle to cut down on the plastic sent to landfill?

Polycarbonate has been commonly used to make the sturdy reusable water bottles that many of us use. Polycarbonate is one of the plastics classed as 'other' in the recycling scheme. It has a recycling code of 7, but not all bottles stamped with a 7 are made from polycarbonate.

Polycarbonate is made of a monomer called bisphenol A (BPA). As the plastic breaks down over time, BPA is released into the water held in polycarbonate bottles, particularly when the bottle is heated or repeatedly washed.

"If you have a bottle made of polycarbonate, on first use there probably isn't much depolymerisation but as you use it again and again — especially if things are warm or hot — then there's a high likelihood that there will be a breakdown of the plastic to release the monomer,".

But just because there is some BPA in the water, it doesn't necessarily mean it's dangerous.

Research in animals has found BPA can cause a range of conditions — such as cancer, diabetes, obesity and reproductive and developmental disorders. Some studies suggest that young animals metabolise BPA less efficiently than adults.

"But there's nothing much in the way of identified effects in humans — virtually all of the effects have been established in relatively higher levels of exposure in animal models. The level of exposure is probably not sufficient to cause these effects [in people]. But people who are feeding young children are saying 'I'd rather not take the chance', which is fair enough."

It's likely that soon we won't need to make these choices ourselves. Even though most national food safety agencies, including Australia's FSANZ, say that the level of exposure to BPA is too low to be dangerous, food and drink companies are moving away from polycarbonate because of the bad press.

However, other agencies, such as the US National Toxicology Program, are worried enough to be carrying out reviews and the World Health Organisation is holding a meeting next month to review all the scientific evidence.

"There is a lot of ongoing work to look at the effects of this compound to see whether this genuinely represents a big issue. The position at present is that it doesn't constitute a huge issue,".

"In effect, except that in the very near future, various agencies will make changes to the tolerable daily intake of BPA,". The internationally agreed Tolerable Daily Intake (TDI) for BPA is currently 0.05 mg per kilogram of body weight per day.

One plastic that can be undoubtedly dangerous for making water bottles is polyvinyl chloride (PVC), which has a recycling code of 3. PVC often has phthalates added to make it flexible — though you can't tell this by looking at the recycling code. Thankfully, PVC is not often used to make water bottles.

Choosing a bottle

If you want to err on the side of caution, We suggest you avoid drinks bottles that have the recycling codes of 3 or 7, particularly for children.

The best bottles to use and reuse are those with the recycling codes 2, 4 and 5. 2 and 4 are made from polyethylene and 5 is made from polypropylene.

"There's absolutely nothing in polyethylene or polypropylene that could be classified as dangerous". But these bottles are more expensive to make, so while they are likely to be found more and more in reusable bottles, PET is likely to be the plastic of choice for single-use bottles for a while to come.

You can also check that reusable bottles say they are 'BPA-free', as some bottles may be made of number 5 plastic but use polycarbonate linings or mouthpieces.

Another rule of thumb is to use clear plastic rather than coloured or opaque because they eliminate small potential risks from colouring agents added to the plastic.

And while stainless steel or aluminium bottles are often considered a safe bet, these still have some issues. Stainless steel can corrode a little over time and while the released iron won't harm you, it'll add an unpleasant taste to your water.

Aluminium can also corrode and release aluminium salts into the water. One way of stopping this is to use a plastic liner, which takes you to square one. The glass is a good, but often impractical.

"In the end, you've got to balance all the issues. I would think that many bottles are safe to use, even PET ones. The only ones I would advise against are PVC and polycarbonate,".

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