Guidelines for Rain Water Harvesting in Hilly Areas by Roof Water Collection System

IS 14961: Scope Overview

IS 14961 covers specifications related to steel and allied materials, referencing several Indian Standards for related products and testing methods. Key points include:

• Referenced IS Codes:

  IS No.	Title
  277:1992	Galvanized steel sheet (plain and corrugated)
  1239 (Part 1):1990	Mild steel tubes and fittings
  1254:1991	Corrugated aluminium sheet
  1536:1989	Centrifugally cast iron pressure pipes
  4984:1995	HDPE pipes for water supply
  12701:1996	Rotational moulded polyethylene water tanks
  14243 (Part 2):1995	Site selection for buildings in hill areas

• Rounding Off Rules:
  Follow IS 2:1960 for rounding test or analysis results, retaining the same significant figures as specified values.

• Scope:
  This standard integrates provisions from referenced IS codes to ensure material compatibility and quality for steel fittings and related products.

No direct formulas or tables are specified in the scope clause; refer to individual referenced IS codes for detailed technical data.

flowchart TD
    A[IS 14961 Scope] --> B[References Other IS Codes]
    B --> C[Steel Sheets & Tubes (IS 277, 1239)]
    B --> D[Aluminium Sheets (IS 1254)]
    B --> E[Pipes & Tanks (IS 1536, 4984, 12701)]
    B --> F[Site Selection Guidelines (IS 14243)]
    A --> G[Rounding Off Rules (IS 2)]

For detailed formulas or tables, consult the respective referenced IS standards.

IS 14961 References Summary

This standard incorporates provisions from the following key Indian Standards:

Additional Notes:

• Rounding Off: Follow IS 2:1960 for rounding test/analysis results, keeping significant figures consistent with specified values.
• These references are integral to IS 14961 and should be consulted for detailed material and testing specifications.
• Always check for the latest editions of these standards for up-to-date compliance.

flowchart LR
    A[IS 14961] --> B[Material Specs]
    A --> C[Testing & Quality]
    B --> IS277[Galvanized Steel Sheets]
    B --> IS1239[Mild Steel Tubes]
    B --> IS1254[Aluminium Sheets]
    B --> IS1536[Cast Iron Pipes]
    B --> IS4984[HDPE Pipes]
    B --> IS12701[Polyethylene Tanks]
    C --> IS2[Rounding Rules]

This ensures comprehensive adherence to material and procedural standards referenced in IS 14961.

IS 14961 does not explicitly define a dedicated "Terminology" clause with formulas or tables. However, key points related to terminology and references are:

• References to Other IS Codes: Terminology and specifications often rely on referenced standards such as:

  • IS 277: Galvanized steel sheets
  • IS 1239 (Part 1): Mild steel tubes
  • IS 1254: Corrugated aluminium sheets
  • IS 1536: Cast iron pressure pipes
  • IS 4984: HDPE pipes
  • IS 12701: Polyethylene water tanks
  • IS 14243 (Part 2): Site selection for hill buildings

• Rounding Off Rules: Numerical results must be rounded per IS 2:1960, maintaining the same significant figures as specified values.

Practical Notes on Terminology Usage:

• Use definitions and dimensions as per referenced IS codes.
• Always confirm the latest editions of referenced standards for updated terminology.
• Technical terms follow ICS codes: 13.060.10 (Building materials) and 13.060.20 (Structural steel).

If you need specific definitions or formulas for a particular material or component, refer to the respective IS code listed above.

flowchart LR
    A[IS 14961 Terminology] --> B[References to IS Codes]
    B --> C[IS 277 - Galvanized Steel]
    B --> D[IS 1239 - Mild Steel Tubes]
    B --> E[IS 1254 - Corrugated Aluminium]
    B --> F[IS 1536 - Cast Iron Pipes]
    B --> G[IS 4984 - HDPE Pipes]
    B --> H[IS 12701 - Polyethylene Tanks]
    B --> I[IS 14243 - Site Selection]
    A --> J[Rounding off per IS 2:1960]

For detailed terminology, consult the referenced IS codes directly.

IS 14961: Roof Water Collection System - Key Points

• Catchment Area: The rooftop acts as the primary catchment surface for rainwater.

• Rainwater Harvesting Volume (V):
  [ V = A \times R \times C ]
  Where:

  • (A) = Roof area (m²)
  • (R) = Rainfall depth (m)
  • (C) = Runoff coefficient (typically 0.8–0.95 for roofs)

• Runoff Coefficient (C): Depends on roofing material:

  • Asbestos sheets: 0.85
  • Concrete: 0.9
  • Tiles: 0.8

• Typical Components (Fig. 1 & 2):

  • Roof catchment
  • Gutters and downpipes
  • First flush diverter (to discard initial dirty water)
  • Storage tank or recharge pit

• Design Considerations:

  • Ensure smooth flow with proper slope (1:100 recommended)
  • Use screens to prevent debris entry
  • Provide overflow outlets

Example Table: Runoff Coefficient for Roof Types

flowchart LR
  Roof[Roof Catchment] --> Gutters[Gutters & Downpipes]
  Gutters --> FirstFlush[First Flush Diverter]
  FirstFlush --> Storage[Storage Tank / Recharge Pit]
  Storage --> Overflow[Overflow Outlet]

This system maximizes rainwater harvesting efficiency as per IS 14961 guidelines for hilly areas.

IS 14961: Catchment Area for Roof Water Harvesting

• Catchment Definition (Clause 4.1):
  The roof top acts as the primary catchment surface for rainwater harvesting.

• Catchment Area (A):
  The effective catchment area is the plan area of the roof from which rainwater is collected.

• Key Formula for Rainwater Harvesting Volume (V):
  [ V = A \times R \times C ] where:

  • ( V ) = Volume of water harvested (liters or m³)
  • ( A ) = Catchment area (m²)
  • ( R ) = Rainfall depth (mm)
  • ( C ) = Runoff coefficient (dimensionless, typically 0.8–0.95 for rooftops)

• Runoff Coefficient (C):

  Roof Type	Runoff Coefficient (C)
  Concrete/Asphalt	0.85 - 0.95
  Tiles/Slates	0.75 - 0.85
  Metal Sheets	0.90 - 0.95

• Treatment of Catchment:
  As per guidelines, rooftops should be cleaned and maintained to avoid contamination and improve water quality.

• Typical Details:
  Refer to Fig. 1 & Fig. 2 in IS 14961 for structural details of collection and conveyance.

flowchart LR
    Rainfall --> Roof[Roof Catchment Area]
    Roof --> Gutter[Gutter]
    Gutter --> Filter[First Flush & Filter]
    Filter --> Storage[Storage Tank]

Summary: Use the plan area of the roof, multiply by rainfall and runoff coefficient to estimate harvestable water. Maintain clean rooftops for effective catchment.

IS 14961: Roof Water Harvesting System – Key Components & Specifications

Key Components (Clause 4.1)

• Roof Top (Catchment Area): Primary surface collecting rainwater.
• Gutters and Downpipes: Channel water from roof to storage.
• First Flush Device: Removes initial dirty runoff.
• Storage Tank: Stores harvested water.
• Filters: Remove debris and impurities.
• Overflow Arrangement: Prevents tank overflow damage.

Important Formula

To estimate rainwater harvest volume (V):

[ V = A \times R \times C ]

Where:

• (A) = Roof catchment area (m²)
• (R) = Rainfall depth (m)
• (C) = Runoff coefficient (typical: 0.8 to 0.95 for concrete/asbestos roofs)

Typical Runoff Coefficients

Storage Tank Sizing

• Depends on water demand and rainfall pattern.
• Should allow for dry spell storage.

flowchart TD
    Roof[Roof Catchment] --> Gutters[Gutters]
    Gutters --> Downpipes[Downpipes]
    Downpipes --> FirstFlush[First Flush Device]
    FirstFlush --> Filter[Filter]
    Filter --> Storage[Storage Tank]
    Storage --> Overflow[Overflow Arrangement]

Note: Refer to Fig. 1 & 2 of IS 14961 for detailed structural drawings.

IS 14961: Roofing Materials - Key Specifications & References

• Roofing Materials Covered:

  • Galvanized iron sheets (IS 277:1992)
  • Corrugated aluminium sheets (IS 1254:1991)
  • Concrete clay tiles, slates, glass fibre sheets (non-deleterious)
  • Thatched roofs with waterproof sheeting (e.g., food-grade LDPE films)

• Important Notes:

  • Use non-toxic paints if painting roofs; water runoff from toxic paints is unsafe for drinking.
  • Roof top acts as the water catchment area for rainwater harvesting.

• Relevant IS Codes for Roofing Materials:

• Waterproofing: Thatched roofs require a waterproof membrane (e.g., LDPE film).

Typical Rainwater Harvesting Roof Catchment Formula

[ Q = A \times R \times C ]

Where:

• (Q) = Runoff volume (liters)
• (A) = Roof area (m²)
• (R) = Rainfall depth (mm)
• (C) = Runoff coefficient (depends on roofing material, typically 0.8–0.95)

Runoff Coefficients for Roofing Materials (Typical Values)

flowchart TD
    A[Rainfall] --> B[Roof Surface]
    B --> C[Runoff Volume Q = A × R × C]
    C --> D[Storage/Harvesting System]

Summary: Use IS 277 & IS 1254 for roofing sheet specs; ensure waterproofing and non-toxic paints; apply runoff formula for water harvesting design.

IS 14961 - Gutters (Clause 4.2.2 & Related)

Materials for Gutters

• Galvanized Iron Sheet: As per IS 277 (1992) - plain or corrugated.
• Other Materials: Wood, bamboo, or Reinforced Cement Concrete (RCC).

Key Specifications:

• Gutters must be durable and corrosion-resistant (GI sheets or RCC preferred).
• Size and slope depend on roof area and rainfall intensity.
• Roof acts as the catchment area (Clause 4.1).

Design Considerations:

• Slope: Minimum slope of 1:100 (1%) to ensure proper drainage.
• Capacity: Based on maximum rainfall intensity and roof area.

Basic Formula for Gutter Flow Capacity (Q):

[ Q = A \times I ]

Where:

• ( Q ) = Runoff volume (liters/sec or m³/s)
• ( A ) = Catchment area (m²)
• ( I ) = Rainfall intensity (m/s or mm/hr converted)

Typical Gutter Dimensions (approximate):

References for Further Design:

• IS 277: Galvanized steel sheets
• IS 1239: Mild steel tubes
• IS 1254: Corrugated aluminium sheets

flowchart LR
    Roof[Roof Catchment Area]
    Gutter[Gutter (GI Sheet / RCC)]
    Downpipe[Downpipe]
    Storage[Tank/Storage]

    Roof --> Gutter --> Downpipe --> Storage

Summary: Use corrosion-resistant gutters sized per runoff volume, slope at least 1%, materials per IS 277 or RCC, and design capacity based on roof area and rainfall intensity.

IS 14961 - Down Pipes: Key Specifications & References

Materials for Down Pipes (Clause 4.2.3)

• Galvanized Mild Steel Pipes: As per IS 1239 (Part 1): 1990
• Cast Iron Pipes: As per IS 1536: 1989
• High-Density Polyethylene (HDPE) Pipes: As per IS 4984: 1995

Typical Specifications:

Design Considerations:

• Diameter and thickness as per IS 1239 or IS 1536 depending on material.
• Ensure adequate slope for drainage (usually 1:100 or as per site conditions).
• Proper jointing and fixing to withstand wind and water loads.

Reference Table for Pipe Sizes (Typical from IS 1239 Part 1):

flowchart TD
    GMS[Galvanized Mild Steel Pipe (IS 1239)]
    CI[Cast Iron Pipe (IS 1536)]
    HDPE[HDPE Pipe (IS 4984)]
    DownPipe[Down Pipe]

    GMS --> DownPipe
    CI --> DownPipe
    HDPE --> DownPipe

Summary: Use IS 1239 for galvanized steel, IS 1536 for cast iron, and IS 4984 for HDPE pipes. Select pipe size and thickness per IS code tables, ensure proper slope and secure fixing for effective drainage.

IS 14961: Storage Tanks - Key Specifications & Guidelines

Types & Materials (Clause 4.2.4)

• Underground tanks: Masonry or RCC with waterproof lining; HDPE tanks per IS 12701.
• Overground tanks: GI sheet (IS 277), RCC, plastic/HDPE (IS 12701), or ferro-cement.

General Design Requirements (Clause 4.3)

• Location: On structurally stable slopes; follow IS 14243 for hill areas.
• Size: Based on daily demand, dry spell duration, catchment area & rainfall.
• Inlet pipe: Minimum 100 mm diameter with 20 mesh (850 micron) nylon screen.
• Contamination prevention: Use foul water diversion or foul flush system.
• Filters: Gravel, sand, or natural fibers (coconut, palm, betelnut).
• Underground tanks: Waterproof lining, hand pump, top ≥300 mm above ground.
• Surface tanks: Elevated platform, bottom outlet with stopcock, tap for withdrawal.
• Provisions:
  • Manhole: 600 mm × 600 mm or 600 mm diameter with cover.
  • Vent/overflow pipe: 100 mm diameter with screen.
  • Drain pipe at bottom.
• Maintenance: Clean & disinfect before use and periodically (chlorine, bleaching powder).

Typical Dimensions (from Figures 1 & 2)

References for Materials & Tanks

Summary Diagram: Storage Tank Components

flowchart TD
    RoofRainwater -->|100 mm pipe, screened| Filter[Filter media: gravel/sand/fiber]
    Filter --> StorageTank[Storage Tank]
    StorageTank --> Overflow[Overflow pipe with screen]
    StorageTank --> Drain[Drain pipe with stopcock

IS 14961: General Requirements - Key Points

• Referenced Standards: IS 14961 incorporates provisions from several Indian Standards, essential for materials and components:

  IS No.	Title
  277:1992	Galvanized steel sheet (plain and corrugated)
  1239 (Part 1):1990	Mild steel tubes and fittings
  1254:1991	Corrugated aluminium sheet
  1536:1989	Centrifugally cast iron pressure pipes
  4984:1995	HDPE pipes for water supply
  12701:1996	Rotational moulded polyethylene water tanks
  14243 (Part 2):1995	Site selection for buildings in hill areas

• Rounding Off Rules:
  Follow IS 2:1960 for rounding numerical values.

  • Round to the same number of significant figures as the specified value.
  • Ensures consistency in test results and calculations.

• General Compliance:
  All test or analysis results must comply with referenced standards and rounding rules.

Summary Table: Rounding Off (IS 2:1960)

This ensures uniformity and accuracy in structural design and material specification under IS 14961.

IS 14961 - Design Considerations: Key Points & Specifications

1. Site & Location

• Tank should be on a structurally stable slope.
• If slope shows distress, follow safety guidelines per IS 14243 (Part 2).

2. Tank Size Determination

Depends on:

• Daily water demand
• Duration of dry spell
• Catchment area
• Rainfall intensity

3. Components & Dimensions

• Down pipe diameter: ≥ 100 mm
• Mesh screen: 20 mesh (850 microns) nylon at inlet to prevent debris
• Manhole: 600 mm × 600 mm or 600 mm diameter with cover
• Overflow pipe: 100 mm diameter, positioned 25 mm below inlet
• Drain pipe: Provided at tank bottom with stopcock

4. Water Quality Control

• Prevent first flush contamination by:
  • Diverting initial rainwater away from tank inlet
  • Installing foul flush system for initial rainwater storage and cleaning
• Filter media: gravel, sand, coconut/palm/betelnut fiber

5. Construction & Maintenance

• Underground tanks: waterproof lining, hand pump, top ≥ 300 mm above ground
• Surface tanks: raised platform, bottom outlet for cleaning, tap for withdrawal
• Periodic disinfection with chlorine or bleaching powder is essential

Formula for Tank Capacity (General)

[ V = A \times R \times C ] Where:

• (V) = Tank volume (liters)
• (A) = Catchment area (m²)
• (R) = Rainfall depth (mm)
• (C) = Runoff coefficient (0.8–0.95 for roofs)

Typical Roof Water Collection Structure (Underground & Overground)

graph LR
A[Roof] --> B[Down Pipe (≥100mm dia)]
B --> C[Mesh Screen (20 mesh)]
C --> D[Filter Media (gravel/sand/fiber)]
D --> E[Water Tank]
E --> F[Overflow Pipe (100mm dia)]
E --> G[Drain Pipe with Stopcock]
E --> H[Manhole (600x600 mm)]

References: IS 14243 (Part 2), IS 277, IS 1239 (

IS 14961: Installation and Maintenance - Key Points

Installation Guidelines (Clause 4.3)

• Site Selection: Tank must be on a structurally stable slope; if slope is unstable, follow IS 14243 (Part 2).
• Tank Size: Depends on daily water demand, dry spell duration, catchment area, and rainfall.
• Down Pipe: Minimum 100 mm diameter with 20 mesh (850 microns) nylon screen to prevent debris.
• First Flush System: Prevents contamination by diverting initial dirty rainwater or using a foul flush system.
• Filter Media: Use gravel, sand, or natural fibers (coconut, palm, betelnut) for filtration.
• Tank Position:
  • Underground tanks: waterproof lining, top at least 300 mm above ground, hand pump recommended.
  • Surface tanks: placed on raised platform, outlet pipe at bottom for cleaning, tap for withdrawal.
• Provisioning:
  • Manhole: 600 mm × 600 mm or 600 mm diameter with cover.
  • Vent/Overflow pipe: 100 mm diameter with screen.
  • Drain pipe at bottom.

Maintenance

• Clean and disinfect tanks before use and periodically (chlorine, bleaching powder, potassium permanganate).
• Drain excess water safely to avoid slope instability.

Typical Dimensions (Fig. 1 & 2)

• Rainwater pipe: Ø100 mm
• Manhole: 600 × 600 mm or Ø600 mm
• Overflow pipe: 100 mm diameter, positioned 25 mm below inlet

Summary Table: Key Dimensions

flowchart TD
    Roof -->|Rainwater| Downpipe[100 mm pipe with screen]
    Downpipe --> FirstFlush[First Flush Device]
    FirstFlush --> Filter[Filter Media (gravel/sand/fiber)]
    Filter --> Tank[Water Storage Tank]
   

IS 14961: Committee Composition & Key Specifications

Committee Composition (Annex A)

The technical committee (Hill Area Development Engineering Sectional Committee, CED 56) includes experts from:

• Academic Institutions: University of Roorkee, IIT Delhi, School of Planning and Architecture
• Government Departments: Public Works, Central Water Commission, Indian Meteorological Dept., Ministry of Railways, Ministry of Surface Transport
• Research Organizations: Central Building Research Institute, Geological Survey of India, National Institute of Hydrology
• Industry & Others: National Buildings Construction Corporation, Building Materials & Technology Promotion Council

Key members include Dr. M. N. Viladkar (Chairman), Shri Sheikh Nazir Ahmed, Shri B. B. Kumar, Dr. R. K. Dubey, and others with alternates.

General Design Requirements (Clause 4.3)

• Tank Location: On structurally stable slope; follow IS 14243 (Part 2) for slope safety.
• Tank Size: Depends on daily water demand, dry spell duration, catchment area, rainfall.
• Downpipe Diameter: Minimum 100 mm with 20 mesh (850 microns) nylon screen.
• Contamination Prevention: Use diversion or foul flush system for first flush rainwater.
• Filter Media: Gravel, sand, coconut/palm/betel nut fiber.
• Underground Tanks: Waterproof lining, hand pump, top at least 300 mm above ground.
• Surface Tanks: Raised platform, drain pipe with stopcock, tap for water withdrawal.
• Manhole: 600×600 mm or 600 mm diameter with cover.
• Vent/Overflow Pipe: 100 mm diameter with screen.
• Disinfection: Clean with chlorine, bleaching powder, or potassium permanganate before use and periodically.

Summary Table: Tank Features

flowchart TD
    A[Rainwater Collection] --> B[Down