Drinking River Water Unsafe?
It very much depends on the river and location along that river. if there is a city upstream who is defecating into the river, you'd better not drink from that river. But drinking from the same river upstream of this city could be totally fine.

Disease transmitted through the faeces were very common in the the 19th century especially in cities that had no system of evacuation of wastes. Now, of course the prevalence of such diseases depends on the type of society and therefore on the era and location.

Generally speaking, it is always best to carry tap water (or bottled water) on you. If you have to drink from a river, be cautious, talk to local people, think of what could live upstream (people, cattle, ...) and always use a good filtration system before drinking from any river.