I accidentally contaminated my water so the dupes were showering in Food Poisoning (so gross!) because I forgot the water purifier doesn't remove germs. They did not get sick, spread the germs to other surfaces, or show as disease vector for Food Poisoning. This gave me an unexpected exploit of not having to keep the germy water separate from the non-germy polluted water I was purifying or heat the water to kill the germs. Clean water still lost germs slowly but even cycling the clean/dirty water in the same tank with a purifier picking up dirty and dumping the clean back in did not cause the germs to spread.
Mix germy polluted and clean water together in the same tank. Put germy clean water into the showers/sinks. Could not find the log file as I started a new colony after I noticed this issue.