Drain Smells Worse After Rain — What Does It Mean?
Drains that smell worse during Bangalore rains indicate sewer gas intrusion or dry traps — a problem a camera inspection resolves.
In Bengaluru commercial properties, drains that smell significantly worse during or after heavy rain are almost always experiencing sewer gas intrusion — a condition caused by pressure differentials in the drain system that monsoon rainfall either creates or amplifies. This is not a cleaning problem; it is a drain system integrity problem that requires professional diagnosis.
What Causes This?
- 1Rainwater entering the drain system creates pressure surges that push sewer gas upward through dry P-traps and into the building
- 2Low atmospheric pressure during Bengaluru monsoon storms reduces the pressure that normally holds sewer gas below floor level
- 3Combined stormwater and sanitary drain systems — monsoon volume overwhelms the system and forces sewage gas back through the sanitary fixtures
- 4Cracked drain pipe joints that are normally sealed by hydrostatic pressure — rainwater pressure changes can temporarily open these joints, allowing gas to escape
- 5Dry traps in infrequently used floor drains — the water seal has evaporated and rain-driven pressure surges push sewer gas through the open trap
How Serious Is This?
Hydrogen sulphide from sewer gas is odorous at extremely low concentrations (as low as 0.5 parts per billion). At concentrations commonly found in buildings with sewer gas intrusion, occupants experience headaches, nausea, and respiratory irritation. Long-term low-level exposure in enclosed spaces such as office washrooms or restaurant preparation areas is an occupational health concern. Solving the intrusion source is a building health obligation.
How Clethorix Fixes It
CCTV camera inspection of all drain lines to identify cracked joints, damaged sections, or areas where the pipe seal is compromised under pressure
Smoke testing of the drain system — smoke is introduced at one point and inspected for escape points at walls, floors, or fixtures to precisely identify all intrusion pathways
P-trap restoration: all floor drains re-filled with water and permanent trap primers fitted to any drain that routinely dries out
Structural repair recommendations for any cracked pipes or offset joints identified during the camera and smoke inspection
Prevention Tips
- Weekly: run water into all floor drains and infrequently used washbasin drains to maintain the water seal in every P-trap
- Consider installing automatic trap primers on any floor drain that dries out regularly — these maintain the water seal continuously without manual intervention
- Schedule a pre-monsoon drain inspection annually to identify and repair any pipe joint cracks before the pressure-change season begins
- Never ignore a post-rain smell — it indicates sewer gas is entering the building and the intrusion pathway needs to be found and sealed
Frequently Asked Questions
Why does my Bangalore office smell like sewage only when it rains?
Is sewer gas in my commercial building a health hazard?
Can adding water to drains fix the problem temporarily?
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