Science Questions

Why does water go off?

Tue, 12th Jan 2016

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Grant Burton asked:

Why does water "go off", and how can you store clean water without it spoiling?

If I leave some dishwater in the sink overnight, or leave pee in the loo for a long period of time it can smell quite lethal. Why is this?

Does water in springs or wells go off in this same way?

I read an article on a tsunami relief project where the Earthship people were building water tanks/rain catchers in villages. How long does the water remain viable? And do you have to add anything to the well? Does adding an alkaline, or fish to water tanks help?

I want to recycle bath water in my garden. Reading some grey water web links, grey water storing is strongly discouraged, because pathogens supposedly multiply and can be harmful. Why is it safe to put immediately on the garden but not store it?

How is water stored/recycled on boats/liners, trains, space ships etc?


Kat Arney put this question to chemist Ben Pilgrim...Water droplets

Ben - It's almost always because there's something in it.  I mean water is an inherently stable molecule.  In fact, they've found water that's 2.6 billion  years old, sort of buried deep under the ground in Canada and nothing's happened to that.  The problem is that if there are small contaminants within the water molecules, sort of microbes, things like that.  Then, over time, if they have the right conditions these microbes can sort of grow and proliferate, and make toxins, and so on.

Kat - So it's not the water - it's the stuff in it!


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If you leave water in a covered stainless pot, or perhaps a glass bottle, it should be good for quite some time.  What you're smelling as bad is organisms that are growing primarily on the impurities in water left over dishwater, unflushed toilets, etc.  Soap plus pot scrubbings can actually be quite nutritious to bugs, as well as plants.

Algae can get into the oddest places, and likes growing in any clear, or translucent containers.  It will impart a specific algae taste to the water, bit isn't particularly harmful.  Keeping your container dark can prevent algal growth.

Water may also be able to promote oxidation of mild steel, or aluminum. 

And, it can leach a plastic flavor from many plastic containers such as bicycle water bottles.

Here in the USA, there are very specific regulations about well design and septic drainfield placement to prevent contamination of one's well with direct surface runoff. 

I think the vast majority of bacteria and microorganisms aren't pathogenic to humans, especially when exposed to organisms in your own household (which you've been previously exposed to).  Of course, there is a group of organisms called "fecal-oral" organisms that are optimized to jump from one host to another with fecal contamination, including the zoonotic feces. 

As far as storing grey water, it probably isn't that bad, although it might develop some objectionable odors, and if uncovered, could also host mosquitoes.  Pouring the water on the ground, and the organisms from brackish water disappear or dry out, and others take over.

Perhaps as humans, we are hard-wired to not drink brackish water, but find forms of irrigation as less objectionable. CliffordK, Fri, 6th Jun 2014

This is really another question but related to the above. You mention water in  plastic bottles - how long can it stay OK and if not for ever why not? I have some stored in case of an earthquake (wets coast Canada) and I don't see why it should go off but people say i should replace it. It's been stored for a few years - if I drink it now will it be harmful;? annie123, Sat, 7th Jun 2014

The main concern with water stored in plastic bottles is that some of the ingredients of the plastic may have leached out into the water over the years.

If you drink the water, you drink these chemicals.

Now whether that water is harmful or not depends on what sort of plastic it is, how it was made, and how has it been stored (presumably higher temperatures would promote more migration of chemicals).

A lot of attention recently has focussed on Bisphenol A, which is an ingredient in polycarbonate plastics. It has been reported to have some estrogen-like behaviour. Some countries think the risk is sufficient to ban its use in baby bottles and similar products, but use in a wide variety of other products is still permitted.

Some concern has also focussed on plasticisers, an ingredient in plastics intended to keep them flexible. These tend to be much smaller and more mobile molecules than the plastic polymer itself.

Drinking water stored in plastic bottles is much less risky than dying of thirst after an earthquake. But if you are worried, and can afford it, refilling the water bottles from the town water supply every few years will reduce the level of any chemicals which have leached out of the plastic.

You wouldn't have this concern if the water were stored in glass bottles - but glass bottles are less likely to survive an earthquake... evan_au, Sat, 7th Jun 2014

Good suggestion re refilling them with tap water. I always drink tap water normally anyway and fill bottles when going out for walks etc. I should have thought of that. Just wouldn't be as sterile as I assume the commercially filled ones should be. annie123, Sat, 7th Jun 2014

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