Tuesday, April 1, 2008

HDPE : The Only Safe Plastic For Drinking Water

It took me about six years of research to discover that there is only one safe tank made of plastic you can stick drinking water in and it is high density polyethylene. This is the same stuff your milk carton is made of.

The only gotcha is that it should be properly "offgassed" when brand new by thoroughly washing it out with a mild disinfectant and allowed to dry out internally in the sun for no more than 48 hours. This cooks off the fresh plastic smell and outgases it has when it is first minted at the factory.

The only water tank superior to this one will have to be made out of stainless steel, which is really expensive. I purchased a secondhand condominium sized boiler before precious metals shot up. Otherwise HDPE is one of the most neutral containers you can store water in long term. If you leave it in long enough it may acquire a mild taste but there is no clinical evidence it will harm you in any way.

Contrast HDPE with almost all other plastics, you will discover that the evidence indicates nobody should be legally permitted to store water in a tank made of say, PVC or even polyvinyl. Less than a year stored in these kinds of containers will leave very nasty by-products. Among other problems, most other kinds of plastics never successfully "offgas." They will have stuff leaching from the interior into the water for twenty years.

I found this fact out (it's safe for water) about HDPE last year when I was reading extensively on the subject and I bought two of these containers on EBay this week. I particularly like how easy they are to modify for the addition of sensors and internal pumps. I've already added a filtration pump (all stainless steel) to one of them through a hole I drilled in the top.

Considering the price difference, I highly recommend these cube containers, as well. Just make absolutely sure of what this container had inside it before it went on sale. If it has had any industrial products (oils, fuels, solvents, etc.) , it is unlikely it will ever be clean enough to use for drinking water. The best ones to buy had food-safe contents or food products in them originally. Even then, you will have to rinse them out thoroughly before you use them. I once saw one of these that contained pickles in vinegar inside and although technically it may have been safe for water I saw no way of ever getting that smell out of the interior.

Of course, stacking this up inside a shelter is not advisable. You would not want 1100 litres of water falling over on you after some kind of ground shock. They do make effective shielding against neutron radiation, if you can figure out a safe way to put them in front of your entrance. I was thinking in some situations it might be possible to roll this in front of the door followed by some smaller containers of water possibly netted on top to keep them in place.


Anonymous said...

I agree with your choice of water tanks. Not trying to pick the flyshit out of the pepper but that tank is rotomolded MDPE or Medium Density Polyethylene.

Medium density is far more common in liquid containers than high density and to my knowledge both are equally safe for drinking water. I have been using an in ground MDPE tank to supply drinking water for 4 years that was designed as a septic tank. It was obviously brand new when I purchased it and it has worked well as an underground water storage unit.

Do not bury a tank that was not designed to be buried as they will crack from flexing in a year or two.

Anonymous said...

Rough idea of price and volume for comparisons?

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rob hudson said...

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AndyPSV said...

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