Taking a shower has nothing to do with preventing Crypto in a pool. The reason to rinse off before going into a pool is to reduce the bather waste. That's something more important for commercial/public pools due to their high bather-load. It's also something one can consider before using their spa if they want their water to last longer between water changes.
In a pool with CYA, then it is difficult to get rid of Cyrpto using chlorine. You'd have to raise the FC to be at least 10 ppm higher than the CYA level to be roughly equivalent to 10 ppm FC with no CYA and in practice to be sure given errors in testing you'd raise the FC to be 20 ppm higher than the CYA level and you'd maintain it that way for 24 hours. While not impossible, this isn't very practical.
It does NOT die out after 10 days in a pool with CYA. They are talking about a pool with no CYA. For a pool at the minimum FC/CYA ratio of 7.5%, this is equivalent to a pool with 0.06 ppm FC and no CYA so with the 15,300 CT value that implies a 99.9% reduction after 177 days (about 6 months). The 10 days they are talking about would require exposure to around 1 ppm FC with no CYA. Remember that our pools have an active chlorine level that is around 17 times lower than this 1 ppm FC with no CYA found in some commercial/public pools and is why the effects on swimsuits, skin, and hair and the rate of disinfection by-products is so much less in our pools than in some commercial/public pools.
It is much easier to just do an emergency remediation dose of sodium chlorite to produce chlorine dioxide from the chlorine in the water and finally the CDC in the Model Aquatic Health Code (MAHC) now talks about that and because it is just for emergencies it's something the EPA won't balk at or at least will let the States do what they want.
Crypto does not get blown in from the air -- it's not like algae spores -- and it is not ubiquitous in soil -- it's not like bacteria. It comes from people and animals though the
Cryptosporidium parvum that infects people almost all comes from other people (i.e. transmission from animals is far less common as the specific protozoan species is different such as
Isospora with cats and dogs and with
Eimeria with cattle though cattle also harbor
Parvum so are the primary infectious source from animals after person-to-person transmission). It is found in the majority of surface water though normally at low levels too low to cause infection (but not always which is why when camping one wants to use either chlorine dioxide or a microfilter).
Crypto specifically gets transmitted through fecal matter discharge usually from diarrhea. This is why this is usually a non-issue for residential pools since you don't normally invite sick people (including kids) with diarrhea to use your pool. It happens in commercial/public pools because some people are irresponsible and go to swim in spite of being sick. The problem with commercial/public pools is that a single sick individual can then infect dozens to hundreds of others and the pathogen can exist for weeks in the pool and patrons carry it from one pool to another if they visit more than one facility.
We have never had a single report of a residential pool having Crypto and I haven't seen any reported in any CDC Surveillance studies in spite of the CDC getting reports from health professionals, not just from commercial/public pools. I'm sure that there may be some instances, but they are very rare. Even the incidence rate in commercial/public pools on a percentage of pools per year basis is quite low. Specifically, out of approximately 300,000 commercial/public swimming pools in the U.S. (vs. around 10 million residential pools roughly evenly split between in-ground and above-ground), the total from 1999-2008 of 122 Crypto outbreaks in treated pools is 0.04% and that's over 10 years (so it's a rate of 0.004% per year). Even the 90 outbreaks reported in 2011-2012 would be a rate of 0.015% per year). Now in terms of numbers of bathers the percentage is higher because one outbreak can affect many bathers, but the point is that not very many pools are affected in spite of the panicked news report (and the CDC is intentionally doing press releases on this because they want the public not to swim when they have diarrhea). It is the main pathogenic issue in chlorinated pools because it is so chlorine resistant, but again I wouldn't worry about it for one's own residential pool. Just avoid inviting anyone over to use the pool that has a gastrointestinal illness particularly with diarrhea. Also note that even most people with diarrhea do not have Crypto.
Now if you really are still concerned in spite of the facts that it's essentially a non-issue for residential pools, then there are several ways of handling it:
- Use an ozone or UV system in the water circulation path. This will NOT prevent immediate transmission of the disease but it will clear the water to the 99.9% reduction after 7 turnovers (so with 6 hour turnovers that's about 2 days running constantly)
- Use a coagulant with fine filtration such as Seaklear PRS Stage 1 and 2
- Superchlorinate for remediation with an FC that is at least 10 and preferably 20 ppm higher than the CYA level for 24 hours (note that this is very harsh so could bleach medium blue vinyl liners)
- Use 2 ppm chlorine dioxide overnight (12 hours) by adding sodium chlorite to a pool with chlorine and CYA in the right amounts
