Sodium Hypochlorite Solutions with Water

It's all about free chlorine, which is what happens when the hypochlorite dissociates.

0.5ppm is commonplace at the exit of a municipal water works and is commonly introduced to stop biology growing in the pipe network. It might be down to 0.2ppm at the tap, as some of the biology that it is there to kill will have died by that point by its action.

2ppm is typical for a municipal swimming pool. The water is safe to drink in biological and chemical terms, though rather unpalatable and can cause vomiting in some individuals.

Free chlorine deals with most single-cell organisms that might cause harm. It cannot affect cryptosporidium, which must be removed by other means.

Sodium hypochlorite, as a liquid, loses its strength over time. Calcium hypochlorite, which is a solid, can be stored practically indefinitely.

As with all chemicals, follow the Materials Safety Data Sheet for best practice on safe storage and handling.

PWSlack has provided a good answer as to use in water treatment plants. However, if you think that is all you need to treat water be warned. Hypochlorination (chlorination) has limits and is intended to be used to control micro-organisms with some caveats. Water treatment plants provide a lot of pretreatment before chlorination is applied and they are regulated in most western countries.

If the water is highly turbid (small particles that can be quantified or observed and are suspended in the water) then the chlorination may not be effective. Bacteria can be harbored in the particle and also protected from the effects of chlorination. Ingestion of the water with bacterial laced particles can be a bad thing. The levels of turbidity in potable water is regulated for public water supply.

If the water contains contamination in the form of organic chemicals, chlorination can create toxic byproducts. Again, these contaminants must be removed before chlorination.

If the water has an elevated level of organic carbon, chlorination may react with it to form Trihalomethane (THM) a suspected precursor to some cancers. The ability to form THM is also related to excessive contact with elevated chlorine levels and organic carbon.

Some metals may react with the chlorinated water to make it less appealing visually.

It is suggested that before you apply chlorination that you obtain a very good set of accredited lab analysis. I would consult with someone versed in professional water treatment and determine what should be sampled, how, what lab, and then have that person give you a good report.There are several factors to consider in addition and relate to pH, temperature and contact times(CT) and a professional is required to answer a particular water demands.

If you are backpacking, and collecting water from local streams, you may want to invest in a good ceramic filter that will filter to at least 1 micron and then use iodine as the choice of disinfection. You can learn more about these filters and iodination from Google. If you want more information on chlorination in water treatment you may want to obtain Clifford White's book on chlorination. Be warned this book is expensive and is intended for professional users. A university library will likely have a copy.