Never included in these discussions on the 1918 flu was the abominable state of public health at the time.
The state of health today presents its own problems, combined with an establishment which both profits and enjoys control over a sick populace (the latter another discussion altogether). I’m not going to outline the history here, but snippet can be garnered at the link.
https://www.cdc.gov/healthywater/drinking/history.html
But influenza is a virus and is not caused by dirty drinking water or lack of sanitation such as cholera and typhoid which are caused by a bacteria.