While true, boiling water kills the bacterias. Not drinking unboiled water is also important part of prevention (thats why beer was known as a perfect way to fight the epidemia, before introduction of modern hygiene and antibiotics. It was the only comon bewerage in which water was boiled and has relatively low alcohol. Still drinking 5+ bottles of beer a day isn't exactly the healthies thing, but better than cholera).
Nevertheless, it's going a bit off-topic. For sure supplying the city with untreated sewage water should cause massive health problems, just not necesserly cholera epidemic.