For a renter, a working STP means less smell near the basement and fewer complaints about drainage from neighbours. Karnataka requires larger apartment complexes to run their own STP, though the exact size that triggers this has moved over time and is reported differently across sources, so we state the rule in words rather than a single confirmed number here. We ask whether a building's STP is actually running, since that decides the smell and the water bill, not the paperwork.
The number
Unknown at level 1 or 2 within budget. Commonly quoted: a 2016 order set the threshold at 20 or more homes, or 2,000 square metres built-up area; a 2024 relaxation is reported to exempt complexes under 120 homes that can connect to the public underground drainage network. Not confirmed against an official KSPCB notice; see _log.md.
Sources
Where it comes from. Level 1 is a government or court page, level 2 established press, level 3 a portal's explainer, which gives only what is commonly quoted.
- KSPCB STP guidelines summary, https://susbio.in/karnataka-state-pollution-control-board-kspcb-stp-guidelines-the-ultimate-guide-for-2025/, level 3
- Thamate, note on regulation of decentralised STPs in Karnataka, https://www.thamate.org/note-on-stps-and-their-implications-for-manual-scavenging/, level 3