But that is not a problem with the water, it's a problem with the container. You are absolutely right, some plastics will leech and some will break down, but assuming you have a magic container that will maintain a sterile seal for eternity, the water inside will be good for eternity also. Pure water is a mixture of two elements and doesnt go bad - ever.Or until a sufficiently harmful substance enters the water in sufficient quantity to cause harm. Many plastics for example will permit many substances to diffuse through them, so if you were to store a plastic container full of water in your garage next to a plastic can of petrol you might find that the petrol taints the water quite quickly. Also many plastics contain harmful substances which can leach out of the container into the contents over long periods of time. Polycarbonates were famous for that quite recently.
Again, not a problem with the water, but stuff that is in it. It might stimulate the growth of algae, but that is a much less common contaminant than bacteria and viruses, both of which are destroyed by ultraviolet light. Also, it might be green (so is cabbage), but is algae actually harmful? I think most species are non-toxic. In any event, sterilise your containers and boil the water before you fill them and nothing will grow. The only issue is whether the container itself is broken down by UV, but again, that is a container problem. Just get the right container. I believe the reason the NATO water bottle is opaque, is not to stop things growing, but because iodine is broken down by UV which stops it working as a sterilising agent. So if you plan on using iodine to sterilise your water, you need a UV opaque container (or mix and keep it in a dark place until the iodine has done it's job).It doesn't. It just helps things grow that are already in the water if it isn't sterile. Green algae being amongst the most obvious, because they're, er, green.
A week in good, direct summer sunshine should kill pretty much all water pathogens. Probably not enough UV in the winter to do the job, but the only real harm is from UV breaking down the plastic and if it's strong enough to do that, it's strong enough to kill the bugs. Bacteria and viruses do not require sunlight to grow BTW, they usually prefer the dark.All correct. Strong enough sunlight will kill anything. However the Earth's atmosphere filters the sunlight very effectively (otherwise we'd all be dead already) and the sunlight needs to be sufficiently strong that it will kill the organisms in the water, rather than promote their growth. We could probably do with more of that sort of sunlight in the UK.
This is one subject I do know about mate, I used to work in a public health laboratory as a medical microbiology technician. It was about 16 years ago and I'm not a world expert or anything, but I've got a clue. I spent 6 months in my own private hell, a department called "Milks & Waters". An unbelievably boring job where I tested milk & water samples for pathogens.
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