Yes, they're often combined, on the basis that it's easier to measure water usage than sewer usage and the latter is presumed to be proportional to the former.
So when people say "my water bill is higher than $X", do they mean the combined bill? Does the town I live in just have abnormally high water prices for an area without water scarcity, or is water just artificially cheap in other places?
Regarding the former - Yes. It's basically something like this:
line 1 - Water usage = X
line 2 - Sewage usage = X * modifier
My monthly water usage is usually something like $20 worth, but my "water bill" is usually around $60-$65 when combining water + sewage (2 adults, $ = USD).
