Cryptosporidium in the Home | YouTube
Insidiously, Crypto is able to get into our personal water supply when the standard drinking water is being contaminated with the sewage overflows, or if a sewage structures are not properly working. Spill over like this are the most common that one could care to admit. The excessive agricultural overflow, bad storms, or will all place a bug squarely in the house.
The most efficient way to treat with the Crypto in the house, then, is to become vigilant. Again, it will mean shunning your mouth and eye contact with the bath water and the shower. Of course, it does not sound really convenient — but this is really far from the impossible, and it is even more of just the habit to get in.
Reference: Quintessential Plumbing | Cryptosporidium in the Home