Is there a feasible alternative to chlorination for public water supplies?

I've searched the net and all I can find is chlorine, but that may only mean that it's the cheapest.

(I've found information on purification of small amounts of water, such as one would need on a camping trip, but I'm looking for answers for large amounts of water.)

The problem isn't so much the purification at the source. Purification at the source, even of large amounts of water, could be feasibly done without chlorine. The problem is that the water then has to travel some distance and still have something in it that will kill anything that seeps in during its journey.
Bromine is used in place of chlorine in some pools because it has less of an odor, but i don't know if it is ever used in drinking water supplies.
I know that chloramines (a nitrogen with three other atoms (hydrogens and chlorines) bound to it... mono-, di- or trichloramine depending on the number of chlorines) are sometimes used. These are less toxic, which may actually make thme more effective at killing some germs. Chlorine reacts quickly with the outside of a bacteria, possible killing it but not reaching the insides. Chloromines aren't reactive enough for as much to be wasted on the outsides... they manage to get inside where they do more damage. This is the same reason that rubbing alcohol is only 70% instead of 100%.
I'm sure there are other alternatives, but i don't know of them off the top of my head.

[This message was edited by methos5000 on 01-03-03 at 02:51 PM.]

try a search for "chloramine" for more info on it (i forgot to mention that since the chlorine is tied up to a nitrogen, it is less likely to react with organic materials in the water to form potentrial carcinogens)... it appears that LA has switched to chloramines: http://www.ladwp.com/water/quality/wq_nh3cl.htm

Chloring dioxide is another alternative with similar benefits to chloramines... try searching for it in google ... here's what the epoa has to say http://www.epa.gov/pesticides/factsheets/chlorinedioxidefactsheet.htm

Thank you, Methos. I want to purify my well water. Department of the environment recommends chlorine (sodium hyperchlorite). I will try to find a supplier for the dioxide or chloramine and use it instead.

You're welcome. I don't know how easy these will be to find or if they're even commercially available, but good luck in your search.
I know it's not important, but the chemist in me had to correct it: sodium hypochlorite.

As often happens, there is now evidence that chloramines, which are used to treat about 1/3 of the US's water, may not be as byproduct-free as once thought. Between 2002 and the present, 5 related byproducts have been found, one of which (iodoacetic acid) is reportedly the most toxic disinfection byproduct ever tested. The upside is that the byproducts appear to be very rare, so chloramines may still be healthier.

read more here

The sodium hypochlorite (bleach) is an effective disinfectant. Most treatment facilities use chlorine gas that reacts in the water to form hypochlorous acid HOCl.. the same ion as the hypoclhorite. Bleach is made more stable by the addition of NaOH to raise the pH.
Monochlormine as Methos has pointed out is becoming more common to limit the Disinfection by products. MonoChloramine NH2CL is the preference as it's odorless and tastless. Dichloramine is the familiar 'pool smell' Trichloramine is not very stable in the range of pH's for drinking..

The American Water Works Association has some really good technical papers on the subject.

Bromine analogs are used in pool treatments for less odor.

Chlorine Dioxide is another option as mentioned

Ozone is also used as the primary disinfectant with Chloramine providing protection in the distribution.

UV light can be used as well but again needs something or continued protection in the distribution system.