The sanitation problem may be one of the worst aspects of the tragedy in New Orleans. Polluted water is full of parasites which once ingested inhabit the digestive tract causing dysentery or even cross over into other organ systems. In a flooded world people are dying of dehydration due to vomiting and diarrhea. The best way to combat bad water is with a large gravity filtration system like the Big Berkey [British Berkefeld ceramic water filter, in a stainless steel housing, made in England] or its plastic cousin filter for a whole family with little effort. Hand filters are good for camping but require a person to spend time every day at the water collection point pumping for all of the days water needs, in an emergency especially when food is restricted plans to eliminate extra exertion must be put into place.
Clean water is not just for drinking but also for food preparation washing of hands and face and washing surfaces and vessels which contact food. If you fear that there are larger parasites such as Giardia or Cryptosporidium. Longer treatment periods are required to kill these parasites. Often, if infected, the treatment for these parasites is Flagyl aka Metronidazole. Speak to your doctor about a prescription for Metronidazole.
Sodium hypochlorite–better known as household bleach–can be used for the following purposes: A 1 in 5 dilution of household bleach with water (1 part bleach to 4 parts water) is effective against many bacteria and some viruses, and is often the disinfectant of choice in cleaning surfaces in hospitals. The solution is corrosive, and needs to be thoroughly removed afterward, so the bleach disinfection is sometimes followed by an ethanol disinfection.
For shock chlorination of wells or water systems, a 2% solution of household bleach is used. For larger systems, HTH is more practical because lower rates can be used. The alkalinity of the sodium hypochlorite solution also causes the precipitation of minerals such as calcium carbonate (lime), so that the shock chlorination is often accompanied by a clogging effect. The precipitate also preserves bacteria, making this practice somewhat less effective. Sodium hypochlorite has been used for the disinfection of drinking water, at a concentration equivalent to about 1 liter of household bleach per 4000 liters of water is used. The exact amount required depends on the water chemistry, temperature, contact time, and presence or absence of sediment. In large-scale applications, residual chlorine is measured to titrate the proper dosing rate. For emergency disinfection, the U.S. EPA recommends the use of 2 drops of 5%ac household bleach per quart of water. [JWR Adds: Be sure to stock up on PLAIN household bleach. Check the label before you buy! The only ingredients should be sodium hypochlorite and water. Formulations with scents added or any other ingredients are probably toxic.]
If infected with intestinal parasites the treatment is Flagyl (aka Metronidazole) Speak to your doctor about a prescription for Metronidazole or the other meds mentioned in the Wikipedia articles.