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IS 11082:1991 is the Indian Standard (BIS) for guidelines for water harvesting. This standard provides guidelines for the planning, design, and implementation of water harvesting systems. It outlines methods for both rooftop and surface runoff harvesting, criteria for assessing water availability, and technical considerations for storage structures, filtration, and water quality maintenance.
Provides guidelines for planning, design, and implementation of rainwater harvesting systems for various applications.
BIM-relevant code. See the BIM Hub for ISO 19650, IFC, and LOD/LOIN frameworks used alongside it.
Practical Notes
! Always incorporate a 'first flush' diverter to prevent initial, more contaminated rainwater from entering the storage system.
! The runoff coefficient is the most critical variable; select it carefully based on the actual surface material and slope as per Table 1 to avoid over- or under-sizing the system.
! Ensure storage tanks are opaque or placed underground to prevent algae growth, and are fully sealed with mosquito-proof vents and overflows.
BS 8515:2009+A1:2013BSI - British Standards Institution, UK
HighCurrent
Rainwater harvesting systems. Code of practice
Covers design, installation, and maintenance of rainwater harvesting systems for non-potable use in buildings.
ARCSA/ASPE/ANSI 63-2018ARCSA/ASPE/ANSI, USA
HighCurrent
Rainwater Catchment Systems Design and Installation
Provides minimum requirements for the design, installation, and maintenance of rainwater catchment systems.
DIN 1989-1:2002-04DIN - Deutsches Institut für Normung, Germany
HighCurrent
Rainwater Harvesting Systems - Part 1: Planning, installation, operation and maintenance
Details requirements for planning, installing, operating, and maintaining rainwater harvesting systems for water conservation.
HB 230-2008Standards Australia, Australia
MediumCurrent
Rainwater Tank Design and Installation Handbook
Provides extensive guidance, similar to the IS code's 'guideline' nature, on system design and installation.
Key Differences
≠IS 11082 is a high-level 'guideline' from 1991, whereas modern international standards (e.g., BS 8515, DIN 1989-1) are detailed 'codes of practice' or standards with legally binding or prescriptive technical requirements.
≠International standards have far more stringent requirements for water quality, filtration, disinfection (e.g., UV), and backflow prevention (e.g., mandatory air gaps) to protect public health and mains water supplies, which are only mentioned conceptually in the IS code.
≠IS 11082 places a significant emphasis on using harvested water for groundwater recharge through structures like percolation pits and trenches, a focus less prominent in international standards which prioritize in-building water use.
≠Modern standards like ARCSA/ASPE/ANSI 63 mandate clear labeling of all rainwater pipes to prevent accidental consumption, a requirement not specified in IS 11082.
Key Similarities
≈All standards are based on the same fundamental system architecture: catchment area, gutters/pipes, first-flush diverter, filter, storage tank, and distribution system.
≈The principle of diverting the initial, more contaminated 'first flush' of rainfall is a core recommendation in both the IS code and all its international counterparts.
≈The basic methodology for sizing the storage tank, based on a water balance of rainfall supply (catchment area, rainfall, runoff coefficient) versus water demand, is a common approach across all documents.
≈All standards universally stress the critical importance of regular maintenance, including cleaning gutters, filters, and tanks, to ensure water quality and system longevity.
Parameter Comparison
Parameter
IS Value
International
Source
First Flush Diversion Guideline
Divert first 10-20 minutes of rainfall, or a depth of 2.5 mm.
Divert a volume based on catchment area, e.g., 0.5 L/m², with a minimum of 20-25 litres.
BS 8515:2009+A1:2013
Runoff Coefficient (Tiled Roof)
0.75 - 0.85 (Clause 4.2.1)
0.8 - 0.9 (depending on pitch and material)
General value in BS 8515 & HB 230
Backflow Prevention (Mains Top-Up)
Advises against cross-connections, but does not specify a device.
Mandates a Type AA or AB air gap to physically separate mains water from rainwater.
BS 8515:2009+A1:2013
Pipework Identification
No specific requirement mentioned.
Mandatory clear labeling (e.g., 'RAINWATER - NOT FOR DRINKING') at set intervals.
ARCSA/ASPE/ANSI 63-2018
Filter Media (Sand Filter)
Specifies coarse sand (1.5-2.0 mm) over gravel (5-10 mm).
Specifies technical requirements for slow sand filters: effective sand size 0.15-0.35 mm, uniformity coefficient < 3.
DIN 1989-1:2002-04
Groundwater Recharge Structures
Provides design guidelines for percolation pits, trenches, and shafts.
Not a primary focus; typically addressed under separate stormwater or sustainable urban drainage systems (SUDS) standards.
General scope of BS 8515 / DIN 1989-1
⚠ Verify details from original standards before use
Key Values5
Quick Reference Values
Runoff coefficient for concrete/asphalt roof0.8 - 0.95
Runoff coefficient for paved areas0.7 - 0.85
Recommended first flush diversion for initial rainfall0.5 - 2 mm
Typical depth of sand filter bed0.6 m - 1.0 m
Minimum cleaning frequency for catchment areaPrior to each rainfall season
Key Formulas
V = A * R * C — Formula for calculating potential harvested water volume, where V is volume, A is catchment area, R is rainfall, and C is runoff coefficient.
Tables & Referenced Sections
Key Tables
Table 1 - Runoff Co-efficients for Various Types of Catchment
Key Clauses
Clause 4 - Assessment of Availability of Water for Harvesting
Clause 5 - Methods of Water Harvesting
Clause 6 - Design Considerations for Storage Structures
How do you calculate the amount of water that can be harvested from a roof?+
Use the formula: Volume = (Catchment Area) x (Rainfall) x (Runoff Coefficient). The runoff coefficient for most roofs is given in Table 1.
What is a 'runoff coefficient'?+
It is the fraction of total rainfall that becomes available as runoff from a surface. For example, a concrete roof has a high coefficient (0.8-0.95), while a lawn has a low one (0.1-0.2) as per Table 1.
Is the water collected from rooftops safe to drink?+
Not directly. It requires filtration and disinfection to meet drinking water standards as per IS 10500. The code provides guidance on basic filtration in Clause 7.
What is the 'first flush' and why is it important?+
The 'first flush' is the initial runoff from a rainfall event, which carries the most debris and pollutants from the catchment surface. Diverting it is crucial for maintaining the quality of the stored water (Clause 7.2).