Well, no water treatment is absolute. Even boiling has the potential (statistical probability) that something will penetrate your natural defenses. ALWAYS! High pressures, and longer cycling times are needed to create completely sterile items. Or, High Radiation (not particulate) will also create sterile water. .
A lot depends on your water supply. What you start with will certainly determine the outcome. The signs are accurate but in many cases are a bit overdone. You are generally subject to all sorts of potential pathogens. Don’t worry about it. If you get sick, most diseases have cures, today. And, they will take a while to manifest…often a week or two, some much longer. The biggest problem with most treatments today is freshness and concentration. But, even a single egg from a trichinosis worm can infect you. And, these are generally very resistant to chemical treatment. Boiling is the safest, but we find many organisms that live in boiling water, again, not really sterile. You would really worry if you studied microbiology. But, for the most part, they work well enough to kill most organisms to let our natural defenses (built up through evolution) work. It is not something I worry about when I am out.
Just take the best precautions you can. Boil water, treat with chemicals, filter stuff with a fine absolute filter, and/or radiate (UV) your water. It still won’t be sterile, but statistics say one in a million will get sick. I will live with those odds.
Read Cafins water treatment series. It is old, but NOT obsolete.
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