Can I Use Salt As Sanitizer Instead of Chlorine?

[chem geek]

catfish,

I have to admit that I am totally lost with your reasoning. Yes, I understand tradeoffs, but when you initially said that high salt levels should kill off pathogens and then I provided information that showed that many pathogens including fecal bacteria can survive (and some thrive) in salt water, you seem to ignore that. Chlorine kills most pathogens very quickly and the most notable exception (mostly in commercial/public pools) is Cryptosporidium parvum. However, I completely am missing your logic of how that one pathogen justifies throwing out chlorine and replacing it with salt water. Crypto is planned to get handled, albeit slowly, via UV or ozone via the circulation system for future commercial/public pools in the U.S. Also, Crypto is usually not an issue in residential pools because it is only introduced into water from a sick individual (usually with diarrhea).

UV or ozone only kill pathogens that get circulated. They do absolutely nothing to pathogens on pool surfaces (bacteria tend to grow best on surfaces and form biofilms that are harder to kill so need to be killed quickly before that happens) and they also do not kill quickly since turnover times are generally measured in hours and it takes 5 turnovers to reach 99.3% of the water under ideal mixing conditions (only 63% of the water goes through the system for each turnover). You have to have a bulk water disinfectant of some sort to prevent both uncontrolled bacterial growth and to prevent person-to-person transmission of disease. Salt water alone doesn't allow for that. If it did, there would be no microscopic life in the ocean and I've already linked to human pathogens that survive in salt water.

As for the surveillance reports I referred to, they were by necessity for commercial/public pools and only for outbreaks since that is all that gets reported. But at least that's some sort of data compared to what you are providing (i.e. nothing at all). Residential pools tend to be safer due to the lower bather-loads and not having sick strangers visit the pool on a regular basis. However, there aren't good statistics about that safety since as you point out people who get sick from their pools will just, at most, go to their doctor and it won't likely get reported to any central government agency (and the doctor probably wouldn't associate the illness with swimming anyway). However, I CAN tell you from the experience of hot tub users that I tracked on poolspaforum.com that there were hot tub itch/rash incidents and one hot tub lung incident and one Legionnaire's Disease that nearly killed the person. I talked to these latter two people and to some of the others and believe me it's heartbreaking. Though most incidents were due to "too low or no chlorine" being used, some were from using "alternative" sanitizers.

Since the science shows that pathogens can live and grow in saltwater and since swimmers in pools are constantly shedding such bacteria (and viruses and sometimes protozoan oocysts) into a relatively smaller volume of water (compared to oceans, lakes and flowing streams), is your point that since there aren't consolidated reports of ill health from residential pools that we should not bother sanitizing them (since just using saltwater wouldn't be much better than fresh water)?

As for kill times, these are measured and well-known. One table of such times for some organisms is in this post where I reference numerous peer reviewed scientific papers in respected journals (though apparently that doesn't carry much weight as far as you are concerned). The kill times for chlorine are VERY fast and this is at a level equivalent to 0.1 ppm Free Chlorine (FC) with no Cyanuric Acid (CYA) so roughly an FC that is 10% of the CYA level. Even at that low chlorine level, fecal bacteria are killed with a 3-log (99.9%) reduction in under 1 minute. Half are killed every 6 seconds. Now in practice, some fecal matter is released in clumped form so it takes somewhat longer. Nevertheless, chlorine is used precisely because it kills faster that almost anything else that is reasonably safe for human exposure. And the greater risk, when it comes to bacteria, is that of uncontrolled growth since larger bacterial concentrations can overwhelm the body's immune system. Also, bacterial safety is also measured in real pools as part of having to pass EPA DIS/TSS-12.

There have been places, such as Australia, that tried using copper/silver since the combination (as you can see from the table) does kill though more slowly. Nevertheless, it is fast enough to prevent uncontrolled bacterial growth. What they found was that this wasn't good enough. It didn't prevent person-to-person transmission of disease and wasn't good at inactivating viruses so they pretty much ban its use in commercial/public pools and give strict warnings to those who want to use this in residential pools. Canada does the same thing.

Now if your argument is about relative risk, you can do whatever you want in your own personal residential pool, but there's no way that commercial/public pools are going to go to salt because all the evidence shows that it is not sanitary. If they go with some kind of alternative, it's not going to be salt, but more likely some other chemical combination like a quarternary ammonium compound along with potassium monopersulfate and with either UV or ozone in the circulation system, but only if they lower their standards for slower kill times.

As for the links of chlorine to bladder and other cancers, and since you have a degree in actuarial science, you should appreciate reading the Environmental Health Criteria 216 "Disinfectants and Disinfectant By-Products" document. The bottom line with the epidemiology studies (including the ones on bladder cancer) is that they varies so some studies showed possible correlations while others did not. Furthermore, in most cases the odds ratios were < 2 and often < 1.5 with wide variations (standard deviation) due to fairly small sample sizes. All of this often means that there are confounding variables not being taken into account.

For example, if someone finds a higher cancer rate for those drinking chlorinated municipal water compared to unchlorinated well water, the correlation may be due to municipal water servicing cities and most well water being in the country where people may do more physical activity. So the real correlation may be with exercise and not with chlorine. It's this kind of effect that makes epidemiological studies dicey unless their odds ratios are high with large sample sizes and having multiple studies looking at a variety of variables (e.g. studies about smoking and lung cancer and other effects).