Reviews > Hydration Systems > Bottles > PET Water Bottle > Owner Review by Roger Caffin

Owner Review - PET Water Bottle
Roger Caffin
updated 5-Aug-2005

Product Information

Product description

This is a polyethylene terephthalate (PET) bottle designed for holding a carbonated beverage - better known as a 'fizzy drink' bottle. The contents in this case were originally sparkling mineral water. Before going any further it is important to distinguish between the two general designs available for soft drinks. The one being reviewed here is designed to hold water under pressure - fizzy drinks. The other sort, which is not being reviewed here, is designed to hold plain water or juice not under pressure. The difference is important.

The base of the bottle typically has five bulges, which seem to have earned for it the name 'rocket base' (the reason for this escapes me). This design is different from the plain water bottle, which has a flat bottom. The reason for the bulges is strength. The bottle is always round, unlike the plain water bottle (which can be square) and the sides of the bottle typically have a few grooves and stiffness rings. Once again the reason for all this is strength. Strength is required to withstand the pressure inside the bottle when it is full of fizzy (carbonated) beverage. There are apparently regulations requiring such pressurised bottles to be able to withstand all sorts of mistreatment without bursting. Indeed, comparing one of these bottles with a plain water bottle does show a significant difference in strength.

The cap on the bottle looks rather small, and the thread inside it looks as though it might fail. However, the thread on the neck of the bottle looks more solid. Inside the cap there is a soft plastic seal to mate with the smooth rim of the neck. The performance of the cap is discussed later.

Technical information on PET

Polyethylene terephthalate or PET is made from ethylene and terephthalic acid - there may well be other manufacturing routes which I do not know. It was invented around 1973, and was first recycled in 1977. It needs to be recycled as it does not bio-degrade significantly, and PET bottle use in America averages about 5.8 kg (12.8 lb) per person per year (frightening). Recycled PET bottles are used for 'Eco-Fleece' and carpets, as well as cheap water bottles. It is classified as an 'engineered' resin, and is considerably more complex and expensive than more simple plastics like High Density Polyethylene (HDPE). However, it has considerable advantages over other plastics in strength, endurance and toxicity. It has been shown to have very low toxicity, with no outgassing or leakage of plasticisers etc (it does not have any). It meets the appropriate FDA regulations for food, fruit juices and drugs (Section 177, 1520 of Title 21 of the US Code of Federal Regulations for Food and Drugs).

There was (or still is) an urban myth running around that refilling these bottles was extremely dangerous. The idea that putting clean water in one of these for a day or two is hazardous, while storing mineral water or Coca Cola (or any of the other strange concoctions people drink) in one for several months is not hazardous, can only be described as 'amusing'. The origin of this story is an unrefereed student thesis from the University of Idaho. In it the student claims to have found traces of the chemical DEHA (diethylhydroxylamine) and that it is a carcinogen. However, DEHA is not used in the manufacture of PET or PET bottles; it is found in some cheap laboratory plastic wares; the levels were at the limit of detection (which is extremely low); not all the tests found any DEHA; and DEHA is not currently classified as a carcinogen by the authorities. It is generally believed that if DEHA was found it probably came from the other lab ware used as a contaminant. One assumes the University was suitably embarrassed. A summary of all this may be found at ENVI-ICPE under 'mythsnrealities'. It is also listed in the Snopes urban myths web site under /toxins/bottles, with other references.

Mind you, if you spit food into one of these bottles every time you drink from it, and never wash the bottle out, I imagine you could get some stuff growing in it. This would apply especially around the threaded neck. But then, that applies to any food container.

The water bottle market place

It is inevitable that one would compare such a 'throw-away' bottle with other water bottles such as an aluminium water bottle (eg Sigg brand) or a plastic (HDPE or Lexan) water bottle (eg Nalgene brand), as shown to the right. Concerns one might have include the possibility of the bottle splitting inside a pack, the cap failing and leaking, and just the fact that the bottle is so light and cheap in comparison. A technical comparison for these as representing typical competitors is given here just to put all the properties of the PET bottle into some sort of context. Costs are very rough. The aluminium bottle is a genuine SIGG one, but rather old. It comes from an era before they started anodising them into bright colours. The rectangular Nalgene bottle 2007-0064 was initially sold as a laboratory bottle, but I had better uses for it.

The final column of cap areas shows values relative to the cap area for the PET bottle. It is there to help understand why the cap on the PET bottle does so well in resisting internal pressure. The area for the pressure to work on is much smaller for the PET bottle than for the Nalgene bottle, so the strength of the thread on the PET bottle can be so much smaller. To be sure, it might be hard putting soup into the narrow neck of a PET bottle, but this review is concerned with carrying water, not soup.

Endurance Testing

Just to see how much abuse they would really take, I took a new (just emptied) PET bottle and gave it an 'extended drop test'. The tests were meant to correspond to a very clumsy person dropping the bottle while handling it. For each landing surface there were three drops onto each of the bottom, side and cap. The test was done with the bottle both full to the brim (no air space) and half full. A full bottle may hit harder, but the absence of air space gives the bottle strength. The results for different landing surfaces are as follows:

Damp sand, from above head height
Apart from a few light surface abrasion marks, the bottle showed no effects at all when either full or half-full. The cap seal remained intact.

Hard lawn, from above head height
The full bottle bounced around a bit, but suffered no harm. Drops with the half full bottle onto the cap resulted in the neck of the bottle being pushed in twice out of three drops. Despite this, the bottle showed no damage once the neck was pulled back out to its normal state. There were no crease marks on the PET which might lead to fractures later on. The cap seal remained intact.

Rock, from chest height
I had some reservations about this test beforehand as it seemed rather harsh. However, the results were interesting. The full bottle bounced high in the air: the result of the elasticity of the PET plastic and the absence of air cushioning. It was rather fascinating to watch. It also meant that each 'drop' gave the bottle several bangs. However, neither the bottle nor the cap seal suffered any harm. The neck was pushed in slightly twice after the drops on the cap, but again the neck popped out with a tug to show no damage. There were some small dents in the rocket-base bulges, but these did not seem to be significant. The half-full bottle behaved quite differently: it gave a 'dead cat' bounce, but the water thrashed around inside. The neck again got pushed in by the drops onto the cap, but again it was restored with no damage.

High drop - thrown way up in the air over hard lawn
Because the bottle was surviving so well, I filled it up again and threw it high in the air several times. The landing position was random of course. The bottle survived three throws without damage, after which I decided to write up these results.

Final state of bottle
The bottle was certainly showing some scratches after all this rough treatment, but I have seen Lexan bottles looking just as bad. The seal was quite intact, and so were the threads. There were small dents on the rocket base bulges, but I have seen these before and the bottles have never leaked there. PET is a very good plastic for this sort of thing. The neck region had been severely mistreated and showed very faint crease marks (only because I knew where to look), but there were no signs of any weakness.

Thread and Seal
The one feature not tested by the drop tests was the reliability of the threads at the neck over the long term. It is clear from the table of cap areas above that the load on the PET bottle cap is smaller than for any of the others. In addition, there is a very good seal material inside the cap. Anyhow, as mentioned below I took two of these bottles on a six week walking tour of the GR10 track in the French Pyrenees in 2002, and used them continuously. I took another two on an 8-week trip along the GR11 on the Spanish side of the Pyrenees in 2004, and again relied totally on them. The threads were still quite intact when we returned home in each case - and the bottles remained in use afterwards for a few more trips. It seems the plastics in both the bottle and the cap are quite robust and abrasion-resistant.

Variants

Our preferred bottle is the 1.25 L (2.6 pt) size for two reasons: we get them free once we have drunk the mineral water in them, and the fairly tall thin design is very robust. But there are many different shapes of PET bottles on the market, and it is worth considering the others in case you have a supply of them.

Coke Bottles, general
These are just as strong but have the 'Coke shape'. If anything the extra bulges may make them slightly stronger, but they may also be slightly heavier. I have never used them so can't really comment.

Larger PET bottles
There are very large Coke and other brand PET bottles, going up to 2 L (4.2 pt) or more. These get their extra volume from an increased diameter. They are strong when full and pressurised, but the larger diameter is weaker once the bottle is only half full and not pressurised. This means they will be susceptible to being crushed in a pack, and that could lead to problems - maybe. I imagine they should be fine if not crushed but we have never used them.

Small PET bottles
Typically these are in the 0.5 - 0.6 L (1 - 1.2 pt) size, are meant for non-fizzy ('still') liquids, and typically they have a fancy dribble top (or 'sports nipple'). Despite being meant for unpressurised use, the small size does mean they are strong enough. They are of course very useful for keeping on the outside of the pack for a quick drink while you walk. In most cases the fancy dribble top can be thrown away and a cap from another PET bottle substituted, for less weight, less volume, and no chance of leaking. The threads are usually compatible.

Non-round PET bottles
These are not reliable. They are meant for the unpressurised or 'still' water or for milk (here in Australia), and can crush fairly easily in the pack. We have used a still water bottle for a while to test it, but had to be very careful when packing. I have done the same drop-test on a rectangular 1 L (2.1 pt) milk bottle, and the lid flew off immediately. Water went everywhere. Since the good PET bottles are essentially free these other sorts are not worth the risk.

Field experience

I typically carry two or three of these PET bottles on all our walking and skiing trips longer than one day without any trouble. Just on principle (partly because they are essentially free anyhow), I replace a bottle after two or three years heavy service. In the last decade or so I have never had any of these PET bottles or bottle caps leak, although I have had heavier Nalgene-class bottles crack and fail in that time (at the lid and at the base). Basically, the regulations which are designed to make your fizzy pop bottle safe to carry home from the supermarket seem to have done a good job!

We have only a limited amount of experience with putting hot water into one of these PET bottles. They do get rinsed with hot water at home quite regularly and withstand that, but washing up water isn't boiling. Once or twice I have put fairly hot water into one of them for my wife to slip into her sleeping bag, and they didn't leak or deform during the night. I have poured left-over boiling water back into a bottle after making morning tea (parts of Australia are a bit dry) and that did not cause any harm. So they seem to take fairly hot water well enough. However, waving an empty one over the flame from a stove can cause some deformation: they are only plastic after all.

Bottles vs Bladders

If I need to carry more than 2 or 3 bottles worth of water at a time I will normally use 2 bottles and a 6 L (12.5 pt) wine cask bladder. The latter is similar to a Platypus or Camelbak bladder, but it's free (once one has drunk the contents of course) and it folds up very small when not in use. It will also hold a lot of water. One might ask why do I carry these bulky bottles which take up lots of space in my pack when empty. My answer has several components. First of all, in my mind space does not matter; weight does. At 43 gm (1.5 oz) each these bottles are light enough compared to my wine cask bladder at 109 g (3.8 oz), and the large commercial bladders are even heavier. Once I decide I need to carry a certain amount of water I have to find that space in my pack, no matter how it is packaged. So that space is available for the bottles, whether they are empty or full. Bottles give me a certain confidence of safety: even if squeezed very hard they aren't going to leak in my pack. The same can't be said for all bladders. By themselves these arguments might not be enough to completely justify the bottles, but my next point is the one which clinches the matter for me. And that is that using a bladder while cooking and living in a tent is so much more difficult than using a bottle. It takes two hands and it is slow. I can grab a bottle, spin the lid off, and pour water in the pot all with one hand, while stirring dinner with the other. Yes, I have tried both approaches, and I find the bottles easier, safer and no heavier.

Following on from the above, how do I compare using a water bottle to using a bladder with a hose while walking? Frankly, I think the whole bladder/hose idea is just another sales bandwagon. The idea that one has to keep drinking during exercise has only come into vogue in the last couple of decades, and it has no research foundation. It's another urban myth, and it too is featured on the Snopes urban myth web site. Go back 20 - 30 years and walkers would have laughed at the idea. One does not need to drink all the time while walking, and in fact excessive drinking or hyponatraemia has caused many deaths in competitive sports. Even in the Australian summer heat my wife and I would go for a couple of hours between drinks, and then we welcome the brief stop to get a bottle out. Finally, by using a bottle rather than a bladder, we have a much better idea of how much water we have drunk and how much we have left. That knowledge can be valuable.

Maintenance

My wife usually gives our PET bottles at least a rinse out with hot water after every trip, and I let them air dry. That's all we do for maintenance. When a bottle starts to look scarred I throw it out and use a new one.

Other Uses - Fuel Storage

One can use some of the other sorts of water bottles for storing fuel (with some care), and PET bottles are also usable. I have seen people carrying these bottles full of alcohol for their stoves, and they do not seem to have had any problems. I have cached these bottles in the shade full of kerosene (Av-Gas or paraffin, not petrol or automotive 'gas') and left them there for some weeks without any problems or loss of fuel. It may be that one could store petrol/gas in them, but this would be rather risky unless one could be sure they would not get damaged and that they would stay very cool. It probably violates some Regulations as well, and I would not recommend it. However, when storing any sort of fuel in these bottles one should make sure the bottles are not stored in with the food: the vapour can migrate slowly through the plastic and taint the food (been there, done that, didn't like it at all).

Summary

Would we keep using them? At that price and weight, need you ask? We do.

Addendum added in 2004

We took four of these bottles to Europe in 2004 for an eight week walking trip in the Pyrenees. They were the only water containers we had for the whole trip. While I have used an Australian wine cask liner (emptied of its original contents of course!) as a hydration bladder on many trips, this time I decided to used just these bottles. All four of them survived in good condition, with no significant damage and no leaks. We even stored red wine in one of the bottles for a little while: the bottle survived, and the wine was fine too.

Biographical information

Backpacking Background

I started bushwalking (the Australian term) at 14, then took up rock climbing at University with the girl who became my wife and is my walking partner. Later on we took up ski touring and canyoning. Winter and summer, we prefer long hard trips by ourselves: about a week in Australia, up to two months in Europe/UK. We prefer fast and light in unfrequented trackless country. We would be out for at least three months a year. Over the last four years we have reduced our pack weights for extended walks from 18 - 20 kg (40 - 45 lb) each to about 12 kg (26 lb), including food. I designed and made much of our lightweight gear myself.

I am also the maintainer of the Australian aus.bushwalking FAQ web site www.bushwalking.org.au/FAQ/.

Reviews > Hydration Systems > Bottles > PET Water Bottle > Owner Review by Roger Caffin