SERVICES

Drainage & Sewerage

Building drainage and sewerage systems

Also calleddrainageseweragestorm waterrainwaterrwh
Related on InfraLens
CODES
IS 1742IS 4111
Definition

Drainage in civil engineering refers to the systems and methods for collecting and conveying excess water away from buildings and infrastructure. Three principal categories: (1) Storm water drainage — surface runoff from roads, roofs, paved areas to prevent flooding and pavement damage. (2) Sewage drainage — wastewater from kitchens, bathrooms, toilets to treatment plants. (3) Sub-surface drainage — groundwater management around foundations, retaining walls, and pavements. Indian Standards: IS 1742 (drainage in buildings), IS 4111 (sewerage and drainage in city areas), IRC 73 (drainage on highways), CPHEEO Manual on Sewerage and Sewage Treatment.

For buildings: storm water and sewage are kept in separate systems per CPHEEO norms. Typical Indian residential drainage: roof downpipes (75-100 mm dia at corners) → channelize to plinth-level chamber → discharge to street storm-water drain. Sewage from toilets / kitchens connects to manholes (at 30 m intervals) leading to a septic tank or municipal sewer. Pipe diameter sized for design flow per CPHEEO: 100 mm for residential single-toilet; 150 mm for multiple-toilet; 200 mm for commercial; 300+ mm for street-side trunks. Slope ensures self-cleansing velocity (>0.6 m/s): 100 mm pipe at 1:60 slope; 150 mm at 1:80; 200 mm at 1:100.

For highways: cross drainage and longitudinal drainage are essential to prevent pavement damage. Cross drainage = transfer of water across the road from cut to fill, via culverts (small-span box or pipe culverts per IRC SP 13:2004). Longitudinal drainage = side drains (open or closed) collecting water from the carriageway. Drainage is designed for the 25-year (urban) or 50-year (highway) return-period storm event. The most-overlooked aspect of Indian drainage design: maintenance access. Buried drainage pipes and culverts develop blockages from siltation, leaves, and construction debris; without manholes at 30 m intervals (per IS 4111), maintenance crews cannot access and clear blockages, causing system failure within 5-10 years.

Where used
  • Building roof and floor drainage — IS 1742
  • Municipal sewerage and storm water (CPHEEO Manual)
  • Highway cross and longitudinal drainage (IRC 73, IRC SP 13)
  • Sub-surface drainage around basements and retaining walls
  • Industrial process drainage and oil-water separation
Acceptance / threshold
Per IS 1742 + IS 4111 + IRC 73: pipe size for design flow at appropriate return period; slope ensures self-cleansing velocity >0.6 m/s; manholes at 30 m intervals; cross-drainage culverts per IRC SP 13.
Site example
Site reality: a Bengaluru residential project's roof drainage was undersized (75 mm pipes for 200 m² roof area in a high-rainfall zone). During monsoon, the system overflowed and water entered the parapet, causing repeated wall seepage and architectural damage. Repair: upsized to 100 mm pipes, added overflow scuppers, and provided proper waterproofing. ₹2.4 lakh fix that ₹15,000 of correct design would have prevented.
Frequently asked
What size of drainage pipe for residential building?
Per CPHEEO norms: 100 mm for single-toilet residential, 150 mm for multi-toilet, 200 mm for commercial. Roof downpipes: 75-100 mm dia at building corners. Self-cleansing slope: 100 mm @ 1:60, 150 mm @ 1:80, 200 mm @ 1:100. Manholes at 30 m intervals on straight runs. Always design for the appropriate design flow (50-year storm for buildings, 25-year for residential pipes).
What is the difference between storm water and sewage drainage?
Storm water drainage handles surface runoff from rainfall (roads, roofs, paved areas) — typically large flows, intermittent, less polluted. Sewage drainage handles wastewater from buildings (toilets, kitchens, bathrooms) — smaller flows, continuous, highly polluted requiring treatment. Per CPHEEO norms, the two are kept in completely separate pipes (CPHEEO Manual on Sewerage). Mixing increases storm-event load on sewage treatment plants and is environmentally undesirable.
What is self-cleansing velocity?
Self-cleansing velocity is the minimum flow velocity that prevents siltation and debris accumulation in drainage pipes. Per CPHEEO + IS 1742: minimum 0.6 m/s for sewage (typical 0.9 m/s for safety margin). Computed by Manning's equation with appropriate slope. Larger pipes need lower slopes to maintain velocity (because cross-section is larger). Inadequate slope causes silt buildup → reduced flow → frequent blockages.
Related services terms
Plumbing & Water Supply
Water supply and plumbing per IS codes
Electrical Installation
Electrical wiring per IS 732, earthing per IS 3043
HVAC & Air Conditioning
Heating, ventilation, air conditioning
Fire Safety
Fire safety per NBC Part 4 and IS codes
Thermal Insulation
Materials and techniques to reduce heat transfer
Acoustic / Sound Insulation
Sound transmission control via materials/design
Septic Tank
Underground anaerobic chamber for primary sewage treatment. Sized at 0.085 m³/person. IS 2470.
Manhole
Vertical access shaft to sewer/drainage line. Spacing 30 m on straight runs, at every junction or bend.