IS 3370:1965 Part 1 is the Indian Standard (BIS) for concrete structures for storage of liquids - general requirements. This code lays down the general requirements for the materials, design, and construction of plain, reinforced, and prestressed concrete structures intended for the storage of liquids, primarily focusing on watertightness and durability.
Lays down general requirements for the design and construction of concrete structures for storage of liquids.
Key reference values — verify against the current code edition / project specification.
| Reference | Value | Clause |
|---|---|---|
| Subject | Concrete liquid-retaining structures — general requirements | Scope |
| Exposure | Severe — stricter durability than IS 456 normal | Design |
| Crack control | Limit crack width (≈ 0.2 mm liquid face) | Serviceability |
| Concrete | Min M30-class, low permeability, low w/c | Materials |
| Read with | IS 3370 Part 2/3/4 / IS 456 / IS 11682 (OHT) | Cross-ref |
IS 3370 (Part 1) is the Indian Standard Code of Practice for Concrete Structures for the Storage of Liquids — Part 1: General Requirements. It is the primary code for any RCC structure that holds water, sewage, or other liquids — including:
The code specifies stricter design requirements than IS 456:2000 for general RCC — because water-retaining structures need durability (zero leakage) AND structural safety. The penalty for failure is service-loss + remedial cost, not collapse.
Note on edition: The historical edition is IS 3370 Part 1:1965 (still cited in older Indian projects). It was significantly revised as IS 3370 Part 1:2021 which introduced limit-state design provisions. Most modern designers use the 2021 edition; older buildings reference the 1965 edition. This note covers the practical content common to both.
Two complementary design approaches are permitted:
(A) Working Stress Method (traditional — IS 3370:1965 era): - Uncracked-section analysis for serviceability - Permissible tensile stresses in concrete LOWER than for general RCC (typically 0.7-1.2 MPa for water-retaining sections, vs 2.5 MPa permitted in IS 456 for ordinary RCC) - The intent: limit cracking at design loads so the structure remains watertight without relying on cracks to be 'self-healing'
(B) Limit State Method (modern — IS 3370:2021): - Limit state of cracking — calculated crack width must be ≤ 0.2 mm (per IS 3370 Part 2:2009 Clause 8) - Stricter than IS 456 limit of 0.3 mm - Allows higher-strength concrete (M30, M35, M40) with more reinforcement to control cracking
Minimum concrete grade (Clause 5.1): - M25 for water-retaining structures (vs M20 minimum for ordinary RCC) - M30 for severe / very-severe exposure - M35 for chemically aggressive environments (sewage, sulphate-rich groundwater)
Minimum cement content (Clause 5.2): - 350 kg/m³ for mild exposure - 360 kg/m³ for severe / very-severe - 400 kg/m³ for chemically aggressive Maximum cement content: 450 kg/m³ (to control shrinkage cracks).
Maximum water-cement ratio (Clause 5.3): - 0.50 for mild exposure - 0.45 for severe / very-severe
Cover (Clause 5.4): minimum 45 mm to all reinforcement (vs 25 mm permitted in IS 456 for mild exposure of ordinary RCC).
Reinforcement (Clause 6): - Maximum bar diameter: 32 mm (smaller spacing of more, smaller bars controls cracking better than fewer, larger bars) - Minimum reinforcement percentage: 0.35% in each face of each direction for non-mass concrete (very high — comparable to IS 456 only for compression members; here it's everywhere) - This minimum-reinforcement rule is the single biggest design implication vs ordinary RCC - Distribution of reinforcement: equal on both faces (water-retaining walls are 'two-way' loaded — water on inside, ground/atmosphere on outside)
Joint locations: Long structures must have construction joints, expansion joints, and contraction joints at specified intervals (Clause 7): - Construction joints: at every pour interface (planned). Use water-stop strip (PVC or rubber per IS 12200). - Contraction joints: at 7.5-10 m intervals in long walls. Full-depth, 8-15 mm wide; sealed with PU sealant + bond breaker. - Expansion joints: at 30-40 m intervals (for very long structures); full-depth, 15-25 mm wide; with sliding bearing details.
Water-stop (Clause 7.2): every joint that crosses the water-retaining surface needs a water-stop: - Centrally-placed PVC water-stop (typical 230 mm wide, 6-9 mm thick) embedded in both pours - Hydrophilic / swelling water-stops for retrofits or repairs - Steel water-stops for high-pressure tanks (rarely used in buildings; common in dam works)
Internal waterproofing (Clause 8): - Surface treatment is supplementary to (not replacement for) structural watertightness - Common approaches: crystalline waterproofing admixtures in mix (e.g., Xypex, Penetron type products); cement-based brushable coatings on inside; epoxy or polyurethane membranes for chemical-resistant tanks - Mandatory test: hydrostatic leakage test per IS 3370 Part 4:2009 — fill the tank, wait 7-14 days, measure leakage. Acceptance: ≤ 5 mm drop over 7 days (uncovered tank) or 2 mm (covered).
Drainage of leaks: even well-designed water-retaining structures occasionally develop micro-cracks. Provide weep holes in the soffit/sides at lowest accessible point and a drainage gutter at the structure perimeter to evacuate any seepage before it damages the surrounding building / foundation.
1. Using IS 456 minimum reinforcement — water-retaining structures need MORE reinforcement (≥ 0.35% each face each direction), not the IS 456 minima. Many designers default to IS 456 and have post-commissioning cracking issues.
2. No water-stop at construction joints — every horizontal joint between pours (wall-to-base, lift-to-lift in tall walls) must have a continuous water-stop. Skipping these is the #1 cause of post-commissioning leakage.
3. Mix design without expert review — water-retaining concrete needs balanced workability + low W/C + adequate cement content + appropriate SCM. Many sites use 'standard M30' off-the-shelf without verification. Test trials are mandatory.
4. No curing for full 14-21 days — water-retaining concrete needs longer curing than ordinary RCC (minimum 14 days, ideally 21+ days). Most sites stop curing at 7 days, leading to surface microcracking that propagates inward.
5. Forgetting thermal effects in mass concrete sections — sections > 1 m thickness (heavy reservoir walls, mat foundations) develop significant heat-of-hydration; differential temperature between core and surface causes early-age cracks. Mitigations: low-heat cement (IS 12330), maximum 350 kg/m³ cement, fly ash replacement (25-35%), cooled mixing water, formwork insulation/removal timing.
6. Backfilling external sides too early — for partially / fully buried tanks, external backfill applies lateral pressure. If applied before concrete has reached full design strength, walls deflect inward (often invisibly) causing internal cracking. Backfill only after 28-day strength is verified and proper curing complete.
7. No hydrostatic test before commissioning — IS 3370 Part 4 mandates a 7-14 day fill test before handover. Many sites skip this and discover leakage 6 months into operation when surrounding finishes / equipment are already damaged.
8. Penetrations through walls without proper sealing — pipes, electrical conduits, drain pipes crossing through walls are leak-points. Use puddle flange or wall-passage assemblies with water-stop collars, not just bituminous mastic at the penetration.
IS 3370 series is a core code for Indian water-infrastructure design — used by water-supply utilities (Jal Boards), sewage treatment authorities, and every building with internal water tanks > 5,000 L capacity.
Edition reality: - IS 3370 Part 1:1965 — historical reference; defines working-stress design philosophy. Cited in older project specs. - IS 3370 Part 1:2021 — current, limit-state-based, integrates with IS 456:2000 and IS 10262:2019. Use this for all new projects. - The Part 1:2021 revision also reorganized content — many design rules previously in Part 1 moved to Part 2. Always check both Part 1 and Part 2:2009 (or its eventual 2025+ revision) for complete design provisions.
Practical reality: water-retaining concrete in India has variable quality. Major Jal Board / MoUD projects (water-treatment plants, large reservoirs) generally meet IS 3370 standards. Private buildings (apartment complex sumps, rooftop tanks) routinely fall short — undertrained labour, inadequate supervision, insufficient curing time. Post-commissioning leakage is the most common Indian building-services failure.
For new water-retaining concrete design: 1. Use IS 3370 Part 1:2021 + Part 2:2009 + IS 10262:2019 2. Specify M30 minimum (M35 for sewage applications) 3. Mandate continuous water-stops at all joints 4. Apply crystalline waterproofing admixture (proven 30-40% reduction in micro-crack permeability) 5. Curing: 14-21 days minimum, with sprinklers or wet hessian — NOT just one-time water sprinkle 6. Hydrostatic leak test before handover (IS 3370 Part 4 protocol) 7. Surface inspection at 6 months and 1 year post-commissioning to catch early-stage leaks
Cost premium of doing this right (vs casual RCC): about 8-15% on the tank cost. Lifecycle saving (avoiding leakage repair which costs 5-20× the original): far exceeds the premium.