Types, Components, Design and Building Drainage
Introduction
Rainwater is an important consideration in architectural planning because every building must provide a controlled path for water falling on its roof, terraces, balconies, paved areas and surrounding site.
A well-designed rainwater disposal system collects runoff, conveys it safely and directs it toward an appropriate destination such as a stormwater drain, recharge system, storage facility, infiltration area, watercourse or other approved outfall.
The system is not simply a network of pipes. It begins with the shape and slope of the roof and continues through rainwater outlets, gutters, downpipes, channels, catch basins, inspection chambers and site drainage. Its final performance depends on how successfully architecture, structure, landscape and building services are coordinated.
In India, the subject also needs to be considered in relation to the applicable building regulations, local authority requirements and relevant Indian Standards. BIS identifies IS 2527:1984 as the code of practice for fixing rainwater gutters and downpipes for roof drainage and IS 1742:1983 as the code of practice for building drainage.
This article explains the complete architectural logic of rainwater disposal—from the roof catchment to the final point of discharge.
What Is a Rainwater Disposal System?
A rainwater disposal system is an arrangement of architectural and drainage components designed to collect, convey, control and safely dispose of rainwater runoff from a building and its surrounding site.
The basic sequence is:
Rainfall → Roof/Site Catchment → Collection → Conveyance → Ground-Level Drainage → Treatment/Storage/Recharge/Disposal
Depending on the project, the final destination may be:
- Rainwater harvesting tank
- Recharge pit or infiltration system
- Surface stormwater drain
- Underground stormwater drainage network
- Detention or retention facility
- Suitable watercourse
- Approved municipal stormwater system
- Landscaped infiltration area
The appropriate solution depends on rainfall, site conditions, soil permeability, building type, local regulations, available infrastructure and the project’s water-management strategy.
Rainwater Disposal vs Rainwater Harvesting
Rainwater disposal and rainwater harvesting are related but are not identical.
Rainwater disposal deals with the safe management and removal of runoff.
Rainwater harvesting intentionally captures and stores or recharges rainwater for beneficial use.
Therefore:
Rainwater harvesting can be one component of a rainwater disposal strategy, but not every rainwater disposal system is a rainwater harvesting system.
For example, a roof may discharge through a downpipe into a stormwater drain. That is rainwater disposal.
If the same roof runoff is filtered and directed to a storage tank for reuse, it becomes part of a rainwater-harvesting system.
For detailed harvesting principles, Archi-Monarch already has dedicated rainwater-harvesting resources; this article focuses primarily on the broader disposal and drainage system.
Why Is Rainwater Disposal Important in Architecture?
Poorly controlled rainwater can affect almost every part of a building.
1. Protection of the building envelope
Uncontrolled runoff can wet walls, parapets, windows and facade finishes.
2. Protection of foundations
Water discharged immediately beside the building can contribute to local saturation, erosion and moisture-related problems.
3. Prevention of roof ponding
Adequate roof falls and drainage outlets reduce prolonged standing water.
4. Protection of circulation areas
Runoff should not create slippery or flooded entrances, ramps, walkways or service areas.
5. Prevention of site flooding
The site drainage network must accommodate runoff from roofs as well as paved and landscaped areas.
6. Integration with water conservation
Where appropriate, runoff can be captured for storage or groundwater recharge instead of being immediately discharged.
7. Protection of adjacent properties
Rainwater should not be discharged in a way that causes dampness, erosion or flooding on neighbouring properties.
Main Components of a Rainwater Disposal System
A building-scale system can contain several components.
| Component | Main Function | Typical Location |
|---|---|---|
| Roof slope | Directs rainwater toward collection points | Roof |
| Rainwater outlet | Collects water from flat/low-slope roofs | Roof |
| Gutter | Collects runoff from sloping roofs | Roof edge |
| Valley gutter | Collects water between roof slopes | Roof valley |
| Scupper | Allows water to pass through a parapet/wall | Roof/parapet |
| Downpipe | Carries rainwater vertically downward | Building facade/service shaft |
| Rainwater head | Collects/distributes water between gutter and pipe | Roof edge |
| Channel drain | Collects surface runoff | Ground/site |
| Catch basin | Receives and collects surface water | Site |
| Inspection chamber | Provides access for inspection/maintenance | Drainage network |
| Stormwater pipe | Carries collected runoff underground | Site |
| Recharge facility | Allows infiltration/recharge | Landscape/site |
| Storage tank | Stores harvested rainwater | Underground/ground/other approved location |
| Overflow | Provides secondary discharge route | Roof/gutter/tank |
The exact components vary according to building type and drainage strategy.
Types of Rainwater Disposal Systems
Rainwater disposal can be classified according to the location from which water is collected and the method used for final management.
1. Roof Rainwater Disposal System
This system manages rainwater falling on the building roof.
It generally consists of:
Roof → Outlet/Gutter → Downpipe → Ground Drain/Harvesting System
It is one of the most important components because the roof often represents a large impervious catchment area.
2. Surface Rainwater Disposal System
This manages runoff from:
- Courtyards
- Roads
- Driveways
- Parking areas
- Plazas
- Footpaths
- Paved terraces
- Hard landscape
Typical components include:
- Surface channels
- Kerb inlets
- Catch basins
- Grated drains
- Linear drains
- Swales
- Stormwater pipes
3. Underground Stormwater Drainage System
Where gravity drainage is possible, collected runoff can be conveyed through underground stormwater pipes.
The network generally includes:
Inlet → Pipe → Inspection Chamber → Branch Drain → Main Drain → Outfall
The pipe network must be coordinated with:
- Foundations
- Basement walls
- Electrical services
- Water-supply lines
- Sewer lines
- Fire-fighting services
- Landscape works
- Road levels
4. Rainwater Harvesting and Recharge System
Instead of immediately discharging runoff, the system can direct suitable rainwater to:
- Storage tanks
- Recharge pits
- Recharge trenches
- Infiltration systems
- Landscaped infiltration areas
The suitability of groundwater recharge depends on local hydrogeology, soil permeability, water quality and applicable regulations.
5. Detention and Retention Systems
For larger developments, runoff may be temporarily stored before controlled discharge.
A detention system temporarily stores water and releases it gradually.
A retention system maintains a permanent or semi-permanent water volume while also providing stormwater-management capacity.
These systems become particularly important where downstream drainage capacity is limited.
Roof Drainage Systems
The roof should be considered a drainage surface rather than an isolated architectural form.
Roof geometry determines where water collects and therefore determines the location of drainage outlets.
Flat and Low-Slope Roofs
Flat or low-slope roofs normally require deliberate falls toward drainage outlets.
Typical arrangements include:
- Internal roof drains
- Parapet outlets
- Scuppers
- Roof gutters
- External rainwater pipes
The designer should avoid creating unintended low points where water can remain trapped.
The location of roof drains should be coordinated with:
- Structural grid
- Beam positions
- Columns
- Waterproofing
- HVAC equipment
- Solar panels
- Maintenance pathways
- Parapets
- Expansion joints
Sloping Roofs
Sloping roofs commonly use:
Roof slope → Eaves gutter → Downpipe → Ground drainage
Depending on the roof geometry, the system may also contain:
- Valley gutters
- Box gutters
- Fascia gutters
- Rainwater heads
- Downpipe outlets
- Overflow provisions
Complex roof forms require particular attention because several roof surfaces may converge at a single drainage point.
Important Roof Drainage Components
1. Gutters
A gutter is a channel that collects runoff from a roof surface and directs it toward an outlet or downpipe.
Gutters may be:
- Eaves gutters
- Box gutters
- Valley gutters
- Parapet gutters
- Concealed gutters
The gutter must be sized for the relevant design rainfall and catchment area.
A gutter that is too small can overflow during heavy rainfall.
2. Rainwater Outlets
Rainwater outlets collect water from flat or low-slope roof surfaces.
They should be positioned at appropriate low points and kept clear of obstructions.
Strainers or guards may be required where leaves and debris could block the drainage opening.
3. Downpipes
A downpipe carries rainwater vertically from a roof drainage system to ground-level drainage or another approved destination.
Downpipe locations should be established during architectural planning rather than added after the facade has been designed.
Architects should coordinate downpipes with:
- Doors
- Windows
- Balconies
- External cladding
- Expansion joints
- Structural columns
- Electrical services
- Fire exits
- Landscape elements
4. Scuppers
A scupper is an opening through a parapet or wall that allows roof water to discharge to the exterior.
Scuppers can be useful for:
- Flat roofs
- Parapet roofs
- Secondary drainage
- Emergency overflow arrangements
Their discharge must be directed so that water does not damage the facade or collect beside the building.
5. Rainwater Heads
A rainwater head is a collection chamber or transition element between a gutter and a downpipe.
It can make inspection and maintenance easier and may also contribute to overflow management depending on the design.
Primary and Secondary Roof Drainage
One of the most important principles in roof drainage is that the primary drainage system should not be the only possible route for water.
A blockage in:
- Outlet
- Gutter
- Strainer
- Downpipe
- Underground drain
can cause water levels to rise.
Where roof geometry could trap water behind a parapet or other raised edge, a secondary or emergency drainage path may be necessary.
International building guidance similarly recognizes secondary emergency drainage as a means of preventing trapped water from damaging a roof or building.
For architectural design, the important principle is:
Emergency overflow should discharge water to a safe and visible location rather than allowing water to enter the building envelope.
The exact sizing and arrangement must follow the applicable local code or engineering standard.
Rainwater Disposal for Different Roof Types
| Roof Type | Common Drainage Arrangement | Main Design Concern |
|---|---|---|
| Flat RCC roof | Roof outlet + downpipe | Adequate falls and outlet placement |
| Low-slope metal roof | Gutter + downpipe | Gutter capacity and overflow |
| Pitched roof | Eaves gutter + downpipe | Catchment and gutter sizing |
| Multi-slope roof | Valley/eaves gutters | Concentrated runoff |
| Parapet roof | Internal outlet/scupper | Emergency overflow |
| Large industrial roof | Gutter + multiple downpipes | Hydraulic capacity and maintenance |
| Green roof | Drainage layer + outlets | Retention, filtration and overflow |
| Terrace roof | Surface falls + outlets | Ponding prevention |
Factors Affecting Rainwater Disposal Design
Rainwater disposal should not be designed using a single universal pipe diameter or gutter size.
The following factors must be considered.
1. Roof Catchment Area
A larger catchment produces a larger potential runoff flow.
The roof should therefore be divided into logical drainage catchments.
2. Rainfall Intensity
Design rainfall intensity varies significantly by location.
A system suitable for a low-rainfall region may be inadequate in an area exposed to intense monsoon storms.
The relevant rainfall data, design duration and return-period criteria should be determined by the responsible drainage engineer in accordance with the applicable standards and authority requirements.
3. Roof Geometry
Complex roofs can concentrate runoff at:
- Valleys
- Internal corners
- Parapets
- Roof intersections
- Low points
These locations require special attention.
4. Roof Slope
The roof must provide a controlled route toward drainage points.
The drainage design should consider both the intended geometric fall and any construction tolerances or structural deflection that could create unintended low spots.
5. Surface Characteristics
Runoff behaviour depends partly on the roof or site surface.
Examples include:
- Concrete
- Metal roofing
- Tiles
- Membrane roofs
- Paved surfaces
- Landscaped surfaces
- Permeable paving
6. Site Topography
The site should be graded so that surface water moves toward intended drainage points.
Architectural site planning should avoid creating:
- Depressions beside buildings
- Reverse slopes toward entrances
- Ponding at ramps
- Water accumulation against basement walls
- Uncontrolled discharge onto neighbouring properties
7. Soil Permeability
Where infiltration or groundwater recharge is proposed, soil and subsurface conditions must be investigated.
A recharge system should not be assumed to work simply because a pit has been provided.
8. Existing Stormwater Infrastructure
The capacity and invert levels of existing municipal or site drainage infrastructure can influence the entire disposal strategy.
Basic Rainwater Disposal Design Process
A practical design workflow can be organized as follows.
Step 1 — Identify catchments
Divide the roof and site into logical drainage areas.
Step 2 — Determine design rainfall
Use the applicable local rainfall information and project design criteria.
Step 3 — Establish drainage points
Locate:
- Roof outlets
- Gutters
- Downpipes
- Surface drains
- Catch basins
Step 4 — Calculate design flow
The responsible engineer should calculate the expected runoff and select appropriate drainage capacities using the applicable method and standard.
Step 5 — Size drainage components
Size:
- Gutters
- Outlets
- Downpipes
- Channels
- Underground pipes
- Chambers
- Storage/recharge components
Step 6 — Provide safe overflow
Consider what happens if the primary drainage path becomes blocked or overwhelmed.
Step 7 — Coordinate with architecture and structure
Check the proposed routes against:
- Beams
- Columns
- Slabs
- Walls
- Facades
- Waterproofing
- Openings
Step 8 — Coordinate with landscape
Integrate drainage with:
- Planting
- Hardscape
- Levels
- Swales
- Recharge areas
- Paving
Step 9 — Verify final discharge
Confirm that the receiving system can accept the proposed discharge and that local authority requirements are satisfied.
Step 10 — Provide maintenance access
The system must be accessible for cleaning, inspection and repair.
Architectural Planning Considerations
Integrate drainage during concept design
One of the common architectural mistakes is designing the complete roof first and attempting to add drainage afterward.
Roof drainage should influence the roof geometry from the beginning.
A good roof plan should answer:
- Where does water collect?
- Where is the lowest point?
- Where are the outlets?
- Where do downpipes run?
- Where does the water go after reaching ground?
- What happens if an outlet blocks?
- Can the system be maintained?
Roof drainage guidance from building institutions similarly emphasizes designing the roof and drainage as an integrated system rather than treating drainage as an afterthought.
MEP and Structural Coordination
Rainwater drainage is an important coordination issue on working drawings and GFC drawings.
Coordinate with structural drawings
Rainwater pipes should be checked against:
- Beams
- Columns
- Slabs
- Shear walls
- Foundations
- Retaining walls
Avoid unnecessary sleeves through structural beams.
Where a rainwater pipe must pass through a slab or wall, the opening, sleeve and waterproofing detail should be coordinated before construction.
Coordinate with MEP
Rainwater pipes should be coordinated with:
- Soil pipes
- Waste pipes
- Vent pipes
- Water-supply pipes
- Fire-fighting services
- HVAC services
- Electrical containment
- Cable trays
The coordination drawing should clearly distinguish rainwater from sanitary drainage.
External vs Internal Rainwater Pipes
External downpipes
External pipes are generally easier to:
- Inspect
- Repair
- Replace
- Detect leaks
However, they affect the building facade and must be integrated aesthetically.
Internal rainwater pipes
Internal systems can provide cleaner facades and may be suitable for certain large or complex buildings.
However, concealed water-carrying pipes require careful detailing because a concealed leak can be difficult to detect and repair.
Their routes should avoid sensitive areas wherever practical.
Rainwater Disposal and Landscape Design
Landscape design can become part of the stormwater-management strategy.
Instead of treating the landscape simply as the final receiving area, designers can use:
- Bioswales
- Rain gardens
- Infiltration areas
- Permeable paving
- Vegetated channels
- Recharge areas
- Detention landscapes
Green infrastructure can slow runoff, promote infiltration and reduce the amount of water entering conventional stormwater infrastructure.
The U.S. EPA identifies rain gardens, permeable pavement, green roofs, infiltration systems and rainwater harvesting as examples of green-infrastructure approaches to stormwater management.
For Indian projects, however, the selected technique must be adapted to local rainfall, soil, groundwater, contamination risk and authority requirements.
Rainwater Disposal in Urban Sites
Urban sites typically contain large areas of impervious surface:
- RCC roofs
- Roads
- Parking
- Concrete paving
- Stone paving
- Plazas
As impervious area increases, more rainfall becomes surface runoff rather than infiltrating naturally.
Therefore, site planning should aim to:
- Reduce unnecessary impervious surfaces.
- Direct runoff toward controlled collection points.
- Provide adequate surface falls.
- Use permeable surfaces where appropriate.
- Integrate landscape-based drainage.
- Provide storage or detention where required.
- Connect to approved stormwater infrastructure.
- Prevent water from accumulating near structures.
Rainwater Disposal in Tall Buildings
Tall buildings require additional coordination because vertical rainwater stacks may extend through many floors.
Important considerations include:
- Vertical pipe alignment
- Pipe diameter
- Hydraulic capacity
- Structural openings
- Pipe supports
- Acoustic control
- Fire-stopping where applicable
- Access for maintenance
- Expansion and movement
- Basement coordination
- Connection to ground-level stormwater drainage
The pipe route should ideally be established early in the planning process.
A poorly coordinated rainwater stack can result in numerous slab openings and service conflicts.
Rainwater Disposal for Basements
Basements are particularly sensitive to uncontrolled water.
Rainwater drainage should prevent surface runoff from entering:
- Basement ramps
- Stair entrances
- Light wells
- Service yards
- Loading areas
- Ventilation openings
Basement ramps should normally have drainage arrangements near the low point, with the exact system determined by site levels and the overall stormwater strategy.
Where gravity discharge is not possible, a suitably designed collection and pumping arrangement may be required.
Materials Used in Rainwater Disposal Systems
Common materials can include:
- uPVC
- HDPE
- Cast iron
- Steel
- Aluminium
- Reinforced concrete
- Masonry channels
- Concrete
- Stainless steel
Material selection should consider:
- Corrosion
- UV exposure
- Temperature
- Structural loading
- Chemical compatibility
- Fire requirements
- Maintenance
- Expected service life
- Connection method
- Local availability
Material suitability must be confirmed against the applicable project specification and standards.
Common Rainwater Disposal Mistakes
1. Designing drainage after the roof
Drainage should be considered during roof planning.
2. Using the same pipe size everywhere
Pipe capacity depends on rainfall, catchment, geometry and hydraulic conditions.
3. Providing too few outlets
A roof with insufficient drainage points can develop concentrated water loading and ponding.
4. Ignoring emergency overflow
A blocked primary outlet can turn a drainage problem into a building-envelope problem.
5. Discharging next to the foundation
Water should be directed to a properly designed receiving system.
6. Mixing rainwater and sanitary drainage without checking regulations
Stormwater and sanitary systems should be treated as separate systems unless a specific approved arrangement allows otherwise.
7. Ignoring maintenance
A drainage system that cannot be cleaned will eventually become a drainage failure.
8. Routing pipes through sensitive spaces
Avoid unnecessary drainage pipe routes through critical rooms or spaces where leaks could cause significant damage.
9. Ignoring site levels
A perfectly designed roof drainage system can still fail at the building level if ground drainage is inadequate.
10. Forgetting adjacent properties
Water should not be discharged in a manner that creates a drainage problem for neighbouring sites.
Maintenance of Rainwater Disposal Systems
Maintenance should be incorporated into the architectural design.
Roof
- Remove leaves and debris.
- Inspect roof outlets.
- Check waterproofing around outlets.
- Check for ponding.
- Inspect overflow openings.
Gutters
- Remove accumulated debris.
- Check gutter falls.
- Inspect joints.
- Check brackets and supports.
- Check for corrosion.
Downpipes
- Inspect joints.
- Check for blockage.
- Check supports.
- Look for leakage.
- Confirm that the outlet remains unobstructed.
Ground drainage
- Clean catch basins.
- Inspect grating.
- Clean chambers.
- Check pipe connections.
- Remove sediment.
Recharge and harvesting systems
- Clean filters.
- Inspect storage tanks.
- Maintain recharge components.
- Monitor overflow arrangements.
Advantages of a Well-Designed Rainwater Disposal System
A properly designed system can:
- Protect the building from water damage.
- Reduce roof ponding.
- Protect facades.
- Reduce uncontrolled site runoff.
- Protect entrances and circulation areas.
- Improve site drainage.
- Support rainwater harvesting.
- Support groundwater recharge where appropriate.
- Reduce maintenance problems.
- Improve building durability.
- Integrate architecture and landscape.
- Improve resilience to heavy rainfall.
Limitations and Challenges
Rainwater disposal design also has several challenges.
Variable rainfall
Rainfall intensity varies by location and storm event.
Limited site space
Dense urban sites may have limited space for open drainage, detention or infiltration.
Existing infrastructure
Municipal drainage may have limited capacity.
Poor soil conditions
Low-permeability soil can make infiltration difficult.
High groundwater
Recharge systems may require additional investigation.
Maintenance
Leaves, sediment and debris can block outlets and drains.
Complex architecture
Irregular roofs and concealed drainage routes can increase design complexity.
Climate uncertainty
Drainage systems should be reviewed for resilience to intense rainfall where applicable to the project’s design criteria.
Rainwater Disposal System vs Rainwater Harvesting System
| Feature | Rainwater Disposal | Rainwater Harvesting |
|---|---|---|
| Main objective | Safely manage runoff | Capture water for reuse/recharge |
| Primary concern | Drainage and discharge | Conservation and reuse |
| Typical components | Gutters, outlets, downpipes, drains | Gutters, filters, tanks, recharge systems |
| Final destination | Drain, outfall, infiltration or approved facility | Tank, recharge system or reuse system |
| Water reuse | Not necessarily | Central objective |
| Flood management | Important | Can contribute |
| Site drainage | Essential | May be integrated |
| Maintenance | Drain cleaning and inspection | Tank/filter and drainage maintenance |
A Simple Rainwater Disposal Flow Diagram
A typical building can be understood as:
ROOF
↓
Roof slope / catchment
↓
Rainwater outlet or gutter
↓
Downpipe
↓
Ground-level catch basin / channel
↓
Inspection chamber
↓
Stormwater drainage network
↓
One or more approved destinations
→ Storage
→ Recharge
→ Detention
→ Surface watercourse
→ Municipal stormwater system
The actual arrangement depends on site conditions and regulations.
Practical Architectural Checklist
Before finalizing a rainwater disposal system, check the following:
Roof
- Roof falls are clearly established.
- All roof catchments have a drainage route.
- Low points are identified.
- Roof outlets are coordinated.
- Overflow provisions are considered.
Building
- Downpipe locations are coordinated.
- Pipes do not conflict with windows and doors.
- Pipe routes are coordinated with structure.
- Sleeves/openings are coordinated.
- Waterproofing details are provided.
Site
- Ground levels direct water appropriately.
- Entrances are protected.
- Basement ramps are drained.
- Catch basins are accessible.
- Site drainage connects to an approved destination.
MEP
- Rainwater and sanitary drainage are clearly identified.
- Pipe sizes are hydraulically checked.
- Vertical stacks are coordinated.
- Maintenance access is provided.
Sustainability
- Rainwater harvesting has been considered.
- Recharge potential has been assessed where appropriate.
- Permeable landscape strategies have been considered.
- Detention or source-control measures have been evaluated where required.
Frequently Asked Questions
What is a rainwater disposal system?
A rainwater disposal system is a network of roof and site drainage components that collects, conveys and safely manages rainwater runoff. It may direct water to a stormwater drain, storage system, recharge facility, infiltration area, watercourse or another approved destination.
What are the main components of a rainwater disposal system?
The main components can include roof slopes, gutters, rainwater outlets, scuppers, rainwater heads, downpipes, surface drains, catch basins, inspection chambers, underground stormwater pipes and an approved final discharge or management facility.
Is rainwater disposal the same as rainwater harvesting?
No. Rainwater disposal focuses on safely managing runoff, whereas rainwater harvesting intentionally captures rainwater for storage, reuse or groundwater recharge. Harvesting can form part of a larger rainwater-disposal strategy.
Why are gutters and downpipes important?
Gutters collect runoff from sloping roofs and direct it toward downpipes. Downpipes then carry the water toward the ground-level drainage or water-management system. Correct sizing and positioning are essential for preventing overflow and uncontrolled discharge.
Why is emergency overflow required?
Emergency overflow provides an alternative route for water when the primary drainage system becomes blocked or overloaded. It is especially important where water could otherwise become trapped behind parapets or within concealed roof drainage systems.
Can rainwater be discharged into a sewer?
The answer depends on the applicable building regulations and local authority requirements. Stormwater and sanitary drainage should not be connected indiscriminately. The designer should verify the approved disposal arrangement for the specific project and jurisdiction.
How should rainwater pipes be coordinated with structure?
Rainwater pipes and sleeves should be coordinated with slabs, beams, columns, walls and foundations before construction. Avoid unnecessary structural penetrations, particularly through beams, and provide properly coordinated sleeve and waterproofing details where penetrations are required.
How is rainwater drainage designed for a building?
The design generally considers catchment area, rainfall intensity, roof geometry, falls, drainage outlets, gutter/downpipe capacity, surface drainage, site levels, receiving infrastructure, emergency overflow and maintenance requirements. The detailed hydraulic design should follow the applicable standards and project criteria.
Conclusion
Rainwater disposal is an essential part of architectural and building-services design. It should not be treated simply as a pipe layout added after the building has been designed.
A successful system begins with the roof and continues through the building envelope, vertical drainage, site grading, stormwater network, landscape and final discharge or water-management facility.
The most important principle is simple:
Every drop of rainwater should have a planned path from the point where it falls to the point where it is safely managed.
For architects, this means coordinating roof geometry, drainage outlets, downpipes, structural openings, waterproofing, site levels and landscape design from the early stages of the project.
Where conditions permit, rainwater harvesting, recharge, infiltration, detention and other source-control measures can be integrated into the drainage strategy. This changes rainwater management from a simple disposal problem into a broader approach to resilient and sustainable site design.
The final system should always be checked against the applicable Indian Standards, NBC provisions, local development/building regulations, municipal requirements and project-specific engineering criteria.