I recently broke 50k population, and all of a sudden my sewage problems have gone buck wild. I have the Sewage Treatment Plant and it has been processing way more sewage than I needed for ages, and suddenly I needed an extra tank. So I plop one and carry on. 5 minutes later I need another tank. 5 minutes after that I need a 3rd tank, and now I do not have anywhere near the money to keep up with this rate (only have income of <5k an hour). My population has only risen to 67k, so why has the sewage trebeled? At 40k a pop these things aren't cheap, and I'm running out of money. I literally can't build anything else.
Why do I keep needing more sewage treatment?