Is it possible to use a UV light to sterilize a bottle of water? If so, what kind of light would be necessary, and how would I go about doing this?
UV radiation can be used to sterilize not to purify it. Milk is (was) pasteurized with UV radiation.
To purify water (removing particulates, minerals, chemicals, etc.) can not be done with UV.
IIRC, the penetration of UV into clear water is about 1 cm; any turbidity will reduce that. The usual sanitization setup for water is a filter, then a flow cell that runs a <1-cm-thick layer of water past a UV emitter in a quartz tube.
Again, that’s IIRC – it’s been years since I’ve looked at the specs for one of these things.
My bad with the title. OP was correct. 
1cm, huh? Next question: how much exposure is needed? Seconds? Hours?
And what sort of light? A special lamp? Or will a blacklight do the trick?
Oh, and a filter is out of the question in this scenario. As is boiling. So I figure I’m left with irradiation of some sort. Not having access to nuclear materials, I figure UV is about it.
Blacklight is lower frequency UV than the bandwidth used for purification of water. The water chambers are constructed to pass water next to the quartz tube containing the light source for sufficient time to effect cleansing. They’re installed on the main distribution branch, so they have to be capable of handling the anticipated flow of the residence. Nametag is correct-turbidity and iron in water will reduce the effecacy of a UV unit, so if an analysis indicates same, a filter upstream is appropriate.
I seem to recall being told that in developing countries, an appropriate way to sterilize water is to leave it in 2 L containers on the roof with black plastic behind it in the sun for a couple days. Is this accurate?
Is it temperature also or is the UV enough - it seems like those 2 L jugs are more than 1 cm thick…
Sounds like they are using temperature.
So where can I find one of the higher-frequency UV lights?
Are you looking to do this to a whole house worth of water, or a drinking water dispenser? If the latter, just grab one that’s already been engineered. One brand I’m aware of is Innowave.
Comemrcial systms are available. I was looking into this for preventing algea blooms (red tide) in a closed loop chilled water system. * The UV lamps can be VERY high power density; the water is used to cool them.
This kills living “stuff” but does nothing for particulates, heavy metals, acid, etc that might still make water non-potable.
*chemical biocides were deemed more cost effective.
UV is much less effective on spore-forming bacteria. These include C. botulinum and other soil borne microbes.
Perhaps chlorine tablets would be more cost effective? bleach?
Just a little bottle
Distill it?
Wont work for my purposes. I want to sterilize a small container of water while leaving the other properties of the water intact (minerals, etc).
Killing bacteria and viruses is the only thing that interests me.
If you just want a few liters, why not sterilze a bottle by autoclave or baking, and shoot water into it through a 100,000MW cutoff ultrafilter? Amicon, Millipore and Cole-Parmer make devices for this or similar purposes.
hmmm… plastic or glass will block the UV in that case.
Try a pond supply store, I have a 9 watt in my pond but they come higher
Also not sure if UV will kill most viruses.
Here is something you may find helpful from this link to an online microbiology textbook. (Bolding mine)
This fits what I recall from micro class, namely that UV light is sometimes used in hospital settings to keep bacterial counts under control on certain surfaces, but not really as a primary means of disinfecting anything. Usually it is part of a whole system, and can be useful in keeping things under control, but is not a magic bullet by any means.