Underground Water Sump (UGT)

Underground water sump (UGT — Under Ground Tank) is a below-ground concrete tank receiving water from utility supply main and pumping to overhead tank (OHT) for distribution. Per IS 3370 (Water-Retaining Concrete) + CPHEEO Manual, sump capacity is typically 3-5 m³ for small residential, 10-50 m³ for commercial, larger for industrial. Located below or adjacent to building, accessed by manhole at ground level.

Design considerations per IS 3370 + CPHEEO: (1) Capacity per CPHEEO LPCD norms (135 LPCD residential, 200 LPCD commercial) × occupancy + 1-day buffer. (2) Concrete grade M25-M30 minimum (water-tight). (3) Wall thickness 200-250 mm; cover ≥ 50 mm against soil. (4) Reinforcement designed for crack-width control per IS 3370 Part 2 (Working Stress Method); typical 0.4-0.6% steel each direction. (5) Waterproofing — internal lining with crystalline (Penetron) or membrane systems. (6) Manhole 600 × 600 mm at ground level for inspection and cleaning. (7) Inlet and outlet penetrations sealed and waterproof. (8) Overflow pipe at top.

For a 4-person residential family at 200 LPCD: daily demand = 800 L; 1-day storage + buffer = 1500-2000 L. Typical sump dimensions: 1.5 × 1.0 × 1.0 m (1500 L) or 2.0 × 1.0 × 1.0 m (2000 L). For commercial 100-person office at 250 LPCD with 2-day buffer: 50 m³ sump = 5.0 × 5.0 × 2.0 m. The most-overlooked aspect of Indian sump construction: waterproofing. Many sumps leak within 5-10 years due to inadequate construction joints + crystalline waterproofing failure; resulting water loss + groundwater contamination. Premium waterproofing systems (₹250-500/m² wall area) extend service to 20+ years.