Rather than rely on purification products' manufacturer's data or reviews of water treatment products that essentially say, "I used this product to purify my water and I didn't get sick." –which could mean the product worked, or the reviewer has a strong immune system, or just as likely that disease pathogens were absent from the water — I opted to research impartial, informed sources.
I found a nice report at the Centers for Disease Control (CDC) website that discussed the efficacy of sodium hypochlorite (NaOCl) (household bleach) against bacteria, protozoa and viruses. NaOCl has long been used as an emergency water treatment and as an alternative to gaseous Chlorine disinfectant in municipal water systems.
The bottom line was that the proper dosage and exposure time to sodium hypochlorite would inactivate all the pathogens except the oocysts of toxoplasma and cryptosporidium. I havenβt found any chemical treatment that completely inactivates these oocysts, but fortunately both are removable by readily available (and portable) sub-micron filters. If chemical treatment is to be relied upon, itβs clear it should be followed by filtering. Filtering alone is not effective because it canβt remove viruses which the bleach will inactivate.
The dosage for clear water recommended by the CDC report was 1.875mgNaOCl/L. The Clorox website recommended a half hour exposure to 2 drops of bleach per liter. I made a calculation based on the weight of 50 drops = approx 3 grams of 6% NaOCl. I calculated that the two drops contain 7.2mg NaOCl. This is significantly higher than the dosages tabulated by the CDC report, but is the same amount as recommended by the Environmental Protection Agency (according to Wikipedia article on chlorine treatment).
Using these numbers, I calculated that a gallon of plain bleach (you don't want to use scented or otherwise modified bleach for disinfecting drinking water) will treat about 31000 liters of water. Clorox costs about $2.50 per gallon making the cost of treatment 0.0075 cents per liter. That means one penny treats 133 liters of water.
As a comparison, I saw 24 chlorine dioxide purification tablets (1 tablet per liter) priced at $14. That comes to 58.3 cents per liter, or treating your water with chlorine dioxide costs 7800 times more than bleach treatment costs. The tablets also require 8 times longer exposure to the pathogens.
Thereβs another advantage to using bleach. You can smell excess bleach. If you donβt smell the bleach after treating the water, it means all the bleach was used and there may be unaffected pathogens remaining. Itβs a good indicator that you need to re-treat.
The big downside of using bleach is the bad taste it imparts to the water. However, after the treatment interval, the bleach can be removed by a charcoal filter. This doesnβt impose an additional burden since all chemically treated water should be filtered to remove oocysts. Just choose a submicron filter that also has a charcoal element. The final result is fresh, clean tasting water at a savings few can ignore.

