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IS 15998 : 2011Rainwater Harvesting Systems - Guidelines

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BS EN 16941-1 · ARCSA/ASPE/ANSI 63 · AS/NZS 3500.3
CurrentFrequently UsedGuidelinesBIMWater Resources · Green Building and Sustainability
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OverviewValues5InternationalTablesFAQ4Related

IS 15998:2011 is the Indian Standard (BIS) for rainwater harvesting systems - guidelines. This standard provides guidelines for planning, designing, constructing, and maintaining rainwater harvesting (RWH) systems. It covers various components like catchment, conveyance, filtration, and storage/recharge, aiming to promote sustainable water management for both new and existing buildings.

Provides general guidelines for the design, construction, and maintenance of rainwater harvesting systems.

Overview

Status
Current
Usage level
Frequently Used
Domain
Water Resources — Green Building and Sustainability
Type
Guidelines
International equivalents
BS EN 16941-1:2018 · BSI / CEN (British Standards Institution / European Committee for Standardization), UK/EuropeARCSA/ASPE/ANSI 63-2018 · ARCSA / ASPE / ANSI (American Rainwater Catchment Systems Association / American Society of Plumbing Engineers / American National Standards Institute), USAAS/NZS 3500.3:2021 · Standards Australia / Standards New Zealand, Australia/New ZealandDIN 1989-1:2002-04 · Deutsches Institut für Normung, Germany
Typically used with
IS 10500IS 4985IS 456IS 1172
Also on InfraLens for IS 15998
5Key values1Tables4FAQs

BIM-relevant code. See the BIM Hub for ISO 19650, IFC, and LOD/LOIN frameworks used alongside it.

Practical Notes
! Always install and maintain a 'first flush' device to prevent the initial, more contaminated runoff from entering the storage tank.
! The runoff coefficient is the most critical variable in calculating harvestable water; choose it carefully based on the actual surface material and slope from Table 1.
! Regularly clean catchment surfaces, gutters, and filters, especially before the monsoon season, to ensure good water quality and system efficiency.
Frequently referenced clauses
Cl. 4Components of Rainwater Harvesting SystemCl. 6Filters and First Flush DevicesCl. 7Storage FacilitiesCl. 8Design of Groundwater Recharge StructuresCl. 9Design ConsiderationsAnnex A - Calculation for Sizing of Rainwater Harvesting System
Pulled from IS 15998:2011. Browse the full clause & table index below in Tables & Referenced Sections.
pipesfiltersconcreteHDPEPVCstorage tanks

International Equivalents

Similar International Standards
BS EN 16941-1:2018BSI / CEN (British Standards Institution / European Committee for Standardization), UK/Europe
HighCurrent
On-site non-potable water systems - Part 1: Systems for the use of rainwater
Covers design, installation, and maintenance of RWH systems for non-potable use, mirroring the Indian Standard's core scope.
ARCSA/ASPE/ANSI 63-2018ARCSA / ASPE / ANSI (American Rainwater Catchment Systems Association / American Society of Plumbing Engineers / American National Standards Institute), USA
HighCurrent
Rainwater Catchment Systems
A dedicated standard for the design, installation, and maintenance of rainwater harvesting systems for both potable and non-potable applications.
AS/NZS 3500.3:2021Standards Australia / Standards New Zealand, Australia/New Zealand
MediumCurrent
Plumbing and drainage - Part 3: Stormwater drainage
Addresses rainwater collection and storage as part of a broader stormwater management framework, including tank and pipe sizing.
DIN 1989-1:2002-04Deutsches Institut für Normung, Germany
HighCurrent
Rainwater harvesting systems - Part 1: Planning, installation, operation and maintenance
A foundational standard covering all aspects of RWH systems, highly influential on other international codes including the BS EN standard.
Key Differences
≠IS 15998 places significant emphasis on groundwater recharge as a primary objective of rainwater harvesting, providing detailed guidelines for recharge pits and trenches. Most international standards (e.g., BS EN 16941-1) focus primarily on storage for on-site use to reduce mains water consumption.
≠The Indian standard is a 'Guideline' and is less prescriptive about component certification and material specifications compared to standards like ARCSA/ASPE 63, which often reference specific NSF/ANSI standards for tanks and components, or BS EN 16941-1 which requires CE marking.
≠IS 15998 describes traditional and simple filtration methods like sand/gravel filters and charcoal filters, reflecting local practices. Western standards tend to focus on manufactured, performance-rated filter units (e.g., vortex filters).
≠International standards like ARCSA/ASPE 63 provide more rigorous and detailed water quality testing protocols and treatment requirements, especially if the water is intended for uses with higher human contact or indoor non-potable uses like toilet flushing and laundry.
Key Similarities
≈All standards recognize the same fundamental system components: catchment surface, gutters/downpipes (conveyance), pre-storage filtration, storage tank, and a distribution mechanism.
≈The principle of diverting the 'first flush' of rainfall, which is typically the most polluted, is a common recommendation across IS 15998 and its international counterparts to improve the quality of stored water.
≈All standards emphasize the critical need for backflow prevention (e.g., via an air gap) where a mains water supply is connected to the rainwater tank as a backup, to protect the public water supply from contamination.
≈The basic methodology for sizing the storage tank is conceptually similar, based on a water balance calculation that considers local rainfall data, catchment area/efficiency, and projected water demand.
≈Safety measures to prevent contamination of stored water, such as ensuring tanks are sealed against sunlight, insects, and vermin, are a common requirement in all standards.
Parameter Comparison
ParameterIS ValueInternationalSource
First Flush Diversion VolumeGuideline of 0.5 to 1.0 mm of rainfall over the catchment area, or the first 10-20 minutes of rain.Recommended 10 gallons per 1,000 sq ft of catchment area (approx. 0.4 mm of rainfall).ARCSA/ASPE/ANSI 63-2018
Mains Water Top-up (Backflow Prevention)Recommends that the mains inlet be above the maximum water level of the tank to prevent backflow.Mandates a specific Type AA or AB air gap compliant with EN 1717 for absolute backflow prevention.BS EN 16941-1:2018
Groundwater Recharge StructuresProvides detailed designs for recharge pits (1-2m wide, 2-3m deep) and trenches filled with graded aggregate.Not typically specified; focus is on storage for use or controlled discharge to municipal stormwater systems.BS EN 16941-1:2018
Tank Inlet DesignRecommends that the inlet pipe discharges near the tank bottom or against the tank wall to avoid disturbing sediment.Specifies use of a 'calmed inlet' device that directs flow upwards, preventing sediment resuspension and aerating the anaerobic zone.BS EN 16941-1:2018
Tank Orifice ScreeningSuggests using a 'net' or 'mesh' on all pipes and openings to prevent mosquito breeding.Specifies corrosion-resistant screen with openings no larger than 1/16 inch (1.59 mm) on all tank penetrations.ARCSA/ASPE/ANSI 63-2018
Eaves Gutter Gradient (Slope)Recommends a slope between 1:100 to 1:50.Specifies a minimum gradient of 1:500, though steeper slopes are common practice.AS/NZS 3500.3:2021
⚠ Verify details from original standards before use

Key Values5

Quick Reference Values
Runoff coefficient for concrete/tiled roof0.80 - 0.95
Runoff coefficient for paved areas (bitumen/concrete)0.70 - 0.85
Runoff coefficient for lawns (sandy soil, <2% slope)0.05 - 0.10
Recommended first flush diversion volume0.5 to 1.0 mm of rainfall
Typical filtration rate for slow sand filters100 - 200 litres/hour/sq.m
Key Formulas
Harvestable Rainwater (m³) = Catchment Area (m²) × Rainfall Depth (m) × Runoff Coefficient

Tables & Referenced Sections

Key Tables
Table 1 - Run-off Coefficients for Various Surfaces
Key Clauses
Clause 4 - Components of Rainwater Harvesting System
Clause 6 - Filters and First Flush Devices
Clause 7 - Storage Facilities
Clause 8 - Design of Groundwater Recharge Structures
Clause 9 - Design Considerations
Annex A - Calculation for Sizing of Rainwater Harvesting System

Related Resources on InfraLens

Cross-Referenced Codes
IS 10500:2012Drinking water specification (second revision...
→
IS 4985:2021Unplasticized PVC (uPVC) pipes for potable wa...
→
IS 456:2000Plain and Reinforced Concrete - Code of Pract...
→
IS 1172:1993Code of basic requirements for water supply, ...
→

Frequently Asked Questions4

How much rainwater can I collect from my roof?+
Volume = Roof Area x Rainfall x Runoff Coefficient. For a concrete roof, the coefficient is 0.80-0.95 (Table 1).
What is a 'first flush'?+
It's the initial, more polluted runoff at the start of a rain shower. The code recommends diverting this water to keep the stored water clean (Clause 6.2).
What are the main components of an RWH system?+
Catchment (e.g., roof), conveyance (gutters/pipes), first flush diverter, filter, and a storage tank or recharge structure (Clause 4).
Is filtration necessary?+
Yes, filtration is essential to remove debris, dust, and contaminants before water is stored or used for recharge. The type of filter depends on the water's intended use (Clause 6).

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