Part of the problem was probably the so-called clean drinking water.
Memo to time travelers: boil water before drinking in most time-places you visit.
Aqueducts.
Actually the issue was probably the density of the population. At its peak Ancient Rome had a population of over 1 million. The proximity made the spread of parasites much easier.
... In addition to that, test the wine for lead...
Or drink wine or low alcohol beer, the old method of assuring safe “drinking water”.