Oh dear squalor...

[guineawolf]

those health building only counter act those percentage to occur plague that cause by squalor

[professorspatula]

The thing with squalor is that is it the only thing that stops population growth. It is a necessary evil. The more squalor, the slower growth becomes, which although also causes unhappiness, does mean you don't have populations reaching insane levels. Things like sewers offset a portion of squalor, so growth may continue to increase. They reportedly help combat the plague too.

You're not really fighting against squalor as such - but population growth itself. You have to try and slow growth in settlements so you reach higher levels of population at a rate you can combat the side effects. So instead of building every farm and population growth boosting building, look at your settlement details scroll and see what the base rate of growth is (include also grain imports). If the base level and any grain imports gives you over 6% growth before other buildings, then adding more farms etc will cause your settlements to grow incredibly fast. The Egyptian cities of Thebes, Alexandria and Memphis are incredibly hard to maintain order in because the growth rate and grain imports are insane. You'll need full garrisons, arenas, massive temples etc just to keep public order around the 75% mark (the magic number that means you don't have riots until it falls below it). You may need to reduce tax rate too, but that makes growth increase further. It's a hard task, and yes, occasionally you feel the need to resort to allowing the city rebel then exterminate the populous.

Squalor may seem like an incredible annoyance but it is necessary, and it adds some challenge to the game. At least the Romans have the best facilities to deal with it. It's the poor barbarians that have no hope!