Ah, the days of summer and the enjoyment of a cool dip in the pool. However, where are you swimming and what is in that pool or hot tub? If it is a public swimming pool, you need to be concerned about organisms, viz. parasites, bacteria and viruses. The Centers for Disease Control warns the public about them because they can cause severe gastrointestinal disease and diarrhea.
58% of the cases reported are caused by the parasite Cryptosporidium which can survive even in a pool that is well-maintained. A small number of swimmers contract pneumonia and others contract a flu-like syndrome from problem organisms.
Disinfectants, when they work, can take days to be effective.
What is a person to do? Not swallowing any of the water is the main recommendation! Check to see if a public pool’s inspection scores are online or at the site.
Pool supply stores and big box stores sell inexpensive test strips, which you can use to test for chlorine and pH. If levels are unsafe, as indicated on the CDC website, don’t swim there.