RAINWATER HARVESTING IN INDIA
1. Meaning of Rainwater Harvesting
Rainwater harvesting (RWH) is the process of collecting, storing and/or recharging rainwater before it is lost as surface runoff.
It has two major purposes:
Storage of rainwater for future use
Recharge of groundwater
Simple Flow
Rainfall → Collection → Filtration → Storage / Groundwater Recharge
The Central Ground Water Board recognises both surface storage for future use and groundwater recharge as major approaches to rainwater harvesting.
Exam Definition
Rainwater harvesting is the collection and management of rainwater for storage or groundwater recharge.
2. Why Do We Need Rainwater Harvesting?
India receives a large amount of rainfall, but the major problem is that rainfall is:
Seasonal
Unevenly distributed
Highly variable
Concentrated in a few months in many regions
Therefore, receiving rainfall does not automatically mean having water throughout the year.
Major reasons
Population growth
Urbanisation
Industrialisation
Increasing water demand
Groundwater over-exploitation
Declining groundwater levels
Increasing paved surfaces
Reduced natural infiltration
Drought
Water scarcity
Increasing agricultural demand
Urban flooding
Seasonal availability of water
CGWB identifies declining groundwater levels, inadequate surface water, reduced infiltration due to urban paving, groundwater-quality improvement through dilution and agricultural/ecological benefits among the reasons for rainwater harvesting.
3. Main Objectives
Rainwater harvesting aims to:
Collect rainwater.
Store water for future use.
Reduce surface runoff.
Increase groundwater recharge.
Raise groundwater availability.
Reduce dependence on external water supplies.
Conserve water.
Reduce soil erosion.
Improve soil moisture.
Reduce urban drainage congestion.
Help manage groundwater depletion.
Support agriculture.
Improve local ecological conditions.
4. Two Major Forms of Rainwater Harvesting
A. Rainwater Storage
Rainwater is collected and stored in:
Tanks
Ponds
Cisterns
Reservoirs
Underground tanks
Purpose
Stored water can subsequently be used for:
Domestic non-potable purposes
Gardening
Irrigation
Livestock
Cleaning
Toilet flushing
B. Groundwater Recharge
Rainwater is directed into the soil/subsurface so that it contributes to groundwater recharge.
Common structures
Recharge pit
Recharge trench
Recharge well
Recharge shaft
Recharge tubewell
Dug-well recharge
Percolation tank
Check dam
Nala bund
Contour bund
Gully plug
Gabion structure
CGWB lists different recharge structures for urban and rural areas.
5. Rooftop Rainwater Harvesting
Definition
Rooftop rainwater harvesting means collecting rainfall falling on the roof of a building and directing it to a:
storage tank, or
groundwater recharge structure.
Basic Sequence
Roof → Gutter → Downpipe → First Flush → Filter → Storage/Recharge
6. Components of Rooftop Rainwater Harvesting
A typical system consists of:
1. Catchment
The roof from which rainwater is collected.
2. Gutters
Channels that collect water from the roof.
3. Downpipes
Pipes carrying water from the gutter to the filter/storage/recharge structure.
4. First-Flush Arrangement
Diverts the initial contaminated runoff.
5. Filter
Removes suspended impurities.
6. Storage Tank
Stores collected rainwater.
7. Recharge Structure
Where groundwater recharge is intended.
8. Overflow Arrangement
Safely disposes of excess water when the storage tank is full.
CGWB technical publications include detailed treatment of catchments, gutters, downpipes, first flush, filters, storage tanks, water quality and design considerations.
7. Catchment Area
The catchment area is the surface over which rainfall is received and from which runoff is collected.
In rooftop harvesting:
Roof = Catchment
Suitable roofs include:
RCC roofs
Metal/tin roofs
Tile roofs
Other suitable relatively impervious roof surfaces
Important
Greater catchment area generally means greater potential water collection.
8. Gutter
A gutter is a channel provided along the edge of a roof to collect rainwater.
Function
Roof → Gutter → Downpipe
9. Downpipe
A downpipe carries water from the gutter to:
first-flush arrangement,
filter,
storage tank,
recharge structure.
The size and arrangement of downpipes depend on factors including roof characteristics and system design.
10. First Flush
Extremely Important for Exams
The first flush is the initial portion of rainfall/runoff that is diverted away from the storage system.
Why?
During dry periods, roofs may accumulate:
Dust
Dirt
Leaves
Bird droppings
Other contaminants
The first rainfall washes many of these materials from the roof.
Therefore:
First flush = diversion of initial roof runoff
MCQ
The first-flush system is primarily designed to:
A. Increase evaporation
B. Divert initial contaminated runoff
C. Increase rainfall
D. Increase groundwater extraction
Answer: B
CGWB technical material specifically explains that dust, dirt and debris accumulated on roofs can contaminate the first runoff and that a first-flush arrangement can divert this water.
11. Filtration
After the first flush, water may be passed through a filtration unit.
Common filter materials include:
Gravel
Coarse sand
Fine sand
Mesh
Other suitable filter media
Important distinction
Filtration ≠ disinfection
Filtration removes many physical impurities but does not automatically guarantee microbiological safety.
If rainwater is intended for drinking, appropriate water-quality testing and treatment/disinfection are necessary.
12. Storage Tank
Collected water can be stored in:
Above-ground tanks
Underground tanks
RCC tanks
Masonry tanks
Plastic tanks
Ferrocement tanks
Important design factors
Roof area
Rainfall
Runoff coefficient
Water demand
Storage period
Tank capacity
Water quality
Available space
13. Overflow
Once the tank becomes full, excess water must be safely diverted.
Overflow can be directed towards:
Recharge pit
Recharge trench
Garden
Suitable drainage system
Infiltration area
14. Recharge Pit
A recharge pit is a relatively shallow structure designed to allow rainwater to infiltrate into the ground.
Suitable for
Houses
Small buildings
Small catchments
Areas with suitable subsurface conditions
Key point
Recharge pit → groundwater recharge
15. Recharge Trench
A recharge trench is a long, narrow excavation designed to facilitate infiltration.
Compared with recharge pit
| Recharge Pit | Recharge Trench |
|---|---|
| Compact structure | Long and narrow |
| Point recharge | Linear recharge |
| Suitable for relatively small catchments | Useful where elongated infiltration area is available |
16. Recharge Well
A recharge well allows water to move into suitable subsurface formations.
It can be useful where:
shallow infiltration is insufficient,
deeper permeable formations exist,
hydrogeological conditions permit recharge.
Important
Recharge wells must be properly designed to avoid groundwater contamination.
17. Recharge Shaft
A recharge shaft is a vertical structure used to facilitate movement of water into deeper permeable formations.
It is particularly useful in some areas where surface soil has limited infiltration capacity.
18. Dug-Well Recharge
Existing dug wells can sometimes be used for groundwater recharge after proper:
filtration,
pretreatment,
site assessment.
Important warning
Do not assume that contaminated runoff can safely be directly introduced into a well.
Poorly designed recharge can contaminate groundwater.
19. Percolation Tank
A percolation tank is a water-storage structure designed primarily to facilitate infiltration/percolation and groundwater recharge.
Exam keyword
Percolation Tank → Groundwater Recharge
20. Check Dam
A check dam is a small barrier constructed across a drainage channel.
Functions
Slows runoff
Temporarily stores water
Reduces erosion
Increases infiltration
Promotes groundwater recharge
Exam keyword
Check Dam → Slow runoff + recharge
21. Gully Plug
A gully plug is a small structure constructed across a gully.
Functions
Reduces runoff velocity
Controls erosion
Promotes infiltration
Conserves soil moisture
22. Contour Bund
A contour bund is constructed approximately along contour lines.
Functions
Reduces runoff
Reduces soil erosion
Conserves soil moisture
Promotes infiltration
23. Contour Trench
A contour trench is a trench constructed along contour lines.
Functions
Intercepts runoff
Reduces runoff velocity
Promotes infiltration
Conserves soil moisture
Reduces erosion
24. Gabion Structure
A gabion structure generally consists of stones enclosed within wire mesh.
Functions
Slows runoff
Reduces erosion
Promotes infiltration
Helps groundwater recharge
25. Important Technical Formula
The basic equation for estimating harvested rainwater is:
Q=PAC
Where:
Q = harvested runoff volume
P = rainfall
A = catchment area
C = runoff coefficient
26. Numerical Example
Suppose:
Roof area = 100 m²
Rainfall = 800 mm
Runoff coefficient = 0.8
Then:
Q=(800/100 x 0.8)/(1000)
Q=64m^3
Therefore:
Harvestable water = 64 m³
Since:
1 m³ = 1,000 litres
Therefore:
Harvestable water = 64,000 litres
27. Most Important Numerical Shortcut
Remember:
1 mm rainfall on 1 m² area = 1 litre of water
Therefore:
100 mm rainfall on 100 m²:
before accounting for the runoff coefficient and other losses.
28. Runoff Coefficient
Not all rainfall becomes collectable runoff.
Some water is:
absorbed,
retained,
evaporated,
infiltrated,
lost through leakage.
Therefore, the runoff coefficient is used.
Higher runoff coefficient
→ More runoff
Lower runoff coefficient
→ Greater losses/infiltration
29. Factors Affecting Rainwater Harvesting
1. Rainfall
Greater rainfall generally means greater harvesting potential.
2. Catchment Area
Larger area → greater potential collection.
3. Roof Material
Different surfaces produce different amounts of runoff.
4. Roof Slope
A suitable slope improves drainage.
5. Rainfall Intensity
High-intensity rainfall can produce large runoff.
6. Runoff Coefficient
Determines collectable fraction of rainfall.
7. Storage Capacity
Determines how much water can be retained.
8. Water Demand
Storage should correspond to expected consumption.
9. Soil Permeability
Important for recharge systems.
10. Hydrogeology
Determines whether recharge is technically suitable.
30. Infiltration
Infiltration is the process by which water enters the soil from the ground surface.
Example
Rain falls on soil.
↓
Some water enters the soil.
↓
This is infiltration.
31. Percolation
Percolation refers to the downward movement of water through soil and subsurface materials.
Memory Trick
Infiltration = enters soil
Percolation = moves downward
32. Groundwater Recharge
Groundwater recharge occurs when water reaches and adds to groundwater storage.
Important
Not every drop that infiltrates immediately becomes groundwater recharge.
Some infiltrated water may:
remain in the soil,
be taken up by plants,
return to the atmosphere through evapotranspiration.
33. Rainwater Harvesting and Groundwater
Rainwater harvesting can:
increase infiltration,
replenish groundwater,
raise groundwater availability locally,
reduce groundwater stress,
improve water security.
CGWB identifies arresting groundwater-level decline and enhancing groundwater availability as important objectives.
34. Urban Rainwater Harvesting
Urbanisation produces large impermeable surfaces:
Concrete roads
Buildings
Parking areas
Pavements
Paved open spaces
Result
Infiltration ↓
Surface runoff ↑
Groundwater recharge ↓
Flooding/waterlogging risk ↑
Therefore, rooftop and stormwater harvesting are particularly important in urban areas.
CGWB specifically identifies reduced infiltration caused by paving in urban areas as a major reason for rainwater harvesting.
35. Rural Rainwater Harvesting
In rural areas, rainwater harvesting is closely connected with:
watershed management,
soil conservation,
agriculture,
groundwater recharge,
moisture conservation.
Important rural structures
Gully plugs
Contour bunds
Gabions
Percolation tanks
Check dams
Nala bunds
Recharge shafts
Dug-well recharge
Groundwater dams/subsurface dykes
These are among the rural approaches identified by CGWB.
36. Traditional Rainwater Harvesting in India
India has a long history of traditional water-harvesting systems.
These systems developed according to:
Local rainfall
Topography
Soil
Geology
Climate
Agricultural requirements
Community needs
37. Khadin
Khadin is a traditional runoff-water harvesting system particularly associated with Rajasthan.
Main idea
Runoff is collected behind an embankment and moisture is conserved in agricultural land.
Exam:
Khadin → Rajasthan
38. Johad
A Johad is a traditional small water-harvesting structure, especially associated with Rajasthan.
Functions
Collect runoff
Store water
Promote groundwater recharge
Support local water availability
Exam:
Johad → Rajasthan
39. Kund / Tanka
Kund and Tanka are traditional rainwater-storage structures associated particularly with arid and semi-arid regions of Rajasthan.
Function
Rainwater storage
Exam:
Kund/Tanka → Rajasthan
40. Guls/Kuls
Guls/Kuls are traditional water channels associated with the Western Himalayas.
They traditionally divert water for agricultural use.
Exam:
Guls/Kuls → Western Himalayas
41. Inundation Channels
Traditional inundation channels were used in flood-prone regions, particularly Bengal, to divert floodwater for agricultural purposes.
Exam:
Inundation Channels → Bengal
42. Traditional Systems — Quick Revision Table
| Traditional System | Region | Main Purpose |
|---|---|---|
| Khadin | Rajasthan | Runoff harvesting/moisture conservation |
| Johad | Rajasthan | Water storage/recharge |
| Kund | Rajasthan | Rainwater storage |
| Tanka | Rajasthan | Rainwater storage |
| Guls/Kuls | Western Himalayas | Water diversion |
| Inundation channels | Bengal | Floodwater diversion/irrigation |
43. Rainwater Harvesting and Agriculture
Rainwater harvesting can support agriculture by:
conserving soil moisture,
increasing groundwater availability,
providing supplementary irrigation,
reducing runoff,
reducing soil erosion,
improving local water availability.
CGWB lists increased agricultural production among the potential benefits of rainwater harvesting/artificial recharge.
44. Rainwater Harvesting and Groundwater Quality
Appropriately designed recharge may improve groundwater quality through dilution in some situations.
However:
Improper recharge can contaminate groundwater.
Therefore:
polluted runoff should not be blindly recharged,
recharge sites require assessment,
filtration and pretreatment may be necessary,
groundwater quality should be monitored.
45. Rainwater Harvesting in Coastal Areas
Over-extraction of groundwater in coastal areas can contribute to saltwater intrusion.
Appropriate groundwater recharge can help maintain freshwater groundwater conditions and may help combat saltwater intrusion.
Exam Statement
Rainwater harvesting can help arrest saltwater intrusion in coastal areas.
Correct — under suitable groundwater-management conditions.
46. Rainwater Harvesting and Urban Flooding
Rainwater harvesting can reduce the quantity of uncontrolled runoff entering:
storm drains,
sewers,
low-lying areas.
Therefore it can contribute to reducing:
waterlogging,
drainage congestion,
local flood pressure.
But:
Rainwater harvesting alone cannot eliminate urban flooding.
It must be combined with proper:
stormwater drainage,
urban planning,
wetlands,
permeable surfaces,
watershed management,
flood management.
47. Advantages of Rainwater Harvesting
Environmental Benefits
Groundwater recharge
Reduced runoff
Reduced erosion
Improved soil moisture
Ecological improvement
Increased vegetation in suitable areas
Economic Benefits
Reduces dependence on external water supplies
Reduces pumping requirements
Can reduce water costs
Provides local water source
Agricultural Benefits
Supplementary irrigation
Soil-moisture conservation
Groundwater recharge
Reduced runoff
Urban Benefits
Reduced runoff
Reduced drainage pressure
Groundwater recharge
Local water availability
48. Limitations
Rainwater harvesting is highly useful but not a universal solution.
Major limitations
Dependence on rainfall
Seasonal rainfall
High initial construction cost in some systems
Maintenance requirement
Limited catchment area
Limited storage capacity
Contamination risk
Unsuitable hydrogeology in some areas
Evaporation from open storage
Poor maintenance
Lack of awareness
Inadequate filtration
49. Maintenance
A rainwater harvesting system requires regular maintenance.
Before Monsoon
Clean roof
Clean gutters
Clean filters
Check pipes
Check first-flush system
Clean storage tank
Inspect recharge structures
During Monsoon
Check leakage
Check first flush
Prevent leaves/debris from entering
Check overflow
After Monsoon
Clean tank
Remove sediment
Inspect recharge structures
Check water quality where necessary
50. Rainwater Quality
Rainwater may be relatively clean at the point of formation, but it can become contaminated during:
atmospheric passage,
roof collection,
storage,
handling.
Potential contaminants include:
Dust
Bird droppings
Leaves
Microorganisms
Roof contaminants
Therefore:
Collected rainwater should not automatically be considered safe drinking water.
Appropriate treatment and testing are required for potable use.
51. Technical Site Selection for Recharge
Before constructing a recharge structure, consider:
Rainfall
Catchment area
Runoff
Soil permeability
Geological formations
Aquifer characteristics
Depth to groundwater
Groundwater quality
Land availability
Existing drainage
Potential contamination sources
CGWB technical guidance emphasises investigation, site selection, planning/design, economic evaluation and monitoring of recharge structures.
52. Hydrogeology and Rainwater Harvesting
This is an important advanced-level concept.
The same recharge structure cannot necessarily be used everywhere.
Why?
Because groundwater conditions differ according to:
rock type,
fractures,
permeability,
aquifer thickness,
depth,
groundwater quality,
geological structure.
Golden Rule
Recharge structure must be selected according to local hydrogeological conditions.
53. Rainwater Harvesting vs Artificial Recharge
Rainwater Harvesting
Broad concept involving:
collection,
storage,
recharge.
Artificial Groundwater Recharge
Specifically means intentionally augmenting groundwater recharge by directing water into suitable subsurface formations.
Exam Trap
“Rainwater harvesting always means groundwater recharge.”
❌ False
Rainwater can also be stored above ground.
54. Rainwater Harvesting vs Water Conservation
Rainwater Harvesting
Capture and utilise/recharge rainfall.
Water Conservation
A broader concept involving:
reducing wastage,
efficient water use,
recycling,
reuse,
harvesting,
improved management.
Exam Point
Rainwater harvesting is a component of water conservation.
55. Rainwater Harvesting vs Watershed Management
| Rainwater Harvesting | Watershed Management |
|---|---|
| Collection/storage/recharge of rainwater | Integrated management of land and water |
| Can be rooftop-based | Landscape/watershed scale |
| May involve one structure | Multiple interventions |
| Focus on rainfall utilisation | Soil + water + vegetation + drainage |
| Component of water management | Comprehensive approach |
56. Government and Institutional Framework
Central Ground Water Board — CGWB
Full form: Central Ground Water Board
It works under the Ministry of Jal Shakti.
Major areas include:
Groundwater assessment
Monitoring
Artificial recharge
Rainwater harvesting
Technical studies
Technical guidance
CGWB maintains manuals and guides relating to artificial recharge and rainwater harvesting.
57. Central Ground Water Authority — CGWA
Full form: Central Ground Water Authority
Important distinction
CGWB = Board
CGWA = Authority
Do not confuse them in examination questions.
CGWA has issued directions and regulatory measures concerning groundwater management and rainwater harvesting in specified contexts.
58. Ministry of Jal Shakti
The Ministry of Jal Shakti is the key Union ministry dealing with water resources and water-related national programmes.
Important areas include:
Water conservation
Groundwater management
River development
Drinking water
Water-use efficiency
Rainwater harvesting
59. Catch the Rain
Catch the Rain is a national water-conservation campaign associated with the National Water Mission, Ministry of Jal Shakti.
Central idea
Catch rainwater where it falls and when it falls.
The programme's knowledge resources include material on artificial recharge, rooftop rainwater harvesting, building bye-laws and groundwater recharge.
60. Master Plan for Artificial Recharge to Groundwater — 2020
The Master Plan for Artificial Recharge to Groundwater in India – 2020 is an important national planning document.
It provides a broad framework for:
identification of suitable areas,
artificial recharge planning,
selection of recharge structures,
consideration of terrain,
hydrogeological suitability.
CGWB lists the Master Plan among its major groundwater-recharge publications.
61. Model Building Bye-Laws
The Model Building Bye-Laws, 2016 issued for guidance of States/UTs contain provisions relating to rainwater harvesting.
The implementation of building regulations ultimately depends on the concerned State Government/Urban Local Body/Urban Development Authority.
Important exam caution
Do not assume that every rainwater-harvesting building rule is identical across India.
State and local regulations can differ.
62. Tamil Nadu and Rainwater Harvesting
Tamil Nadu is a particularly important example in Indian competitive examinations for promoting/making rooftop rainwater harvesting compulsory through its policy and regulatory framework.
Exam memory
Tamil Nadu → Famous Indian example of compulsory/promoted rainwater harvesting
63. Important Standards and Technical Documents
For advanced examination preparation, remember that India's rainwater-harvesting framework includes technical guidance such as:
IS 15797:2008 — Rooftop Rainwater Harvesting Guidelines
Manual on Artificial Recharge
Guide on Artificial Recharge to Groundwater
Master Plan for Artificial Recharge to Groundwater — 2020
Rainwater Harvesting and Conservation Manual
These resources are listed in the National Water Mission's knowledge centre.
64. VERY IMPORTANT DIFFERENCES
Catchment vs Watershed
Catchment: Area from which water is collected/drained.
Watershed: Area draining towards a common outlet.
Storage vs Recharge
Storage: Water retained in tanks/ponds/reservoirs.
Recharge: Water added to groundwater storage.
Infiltration vs Percolation
Infiltration: Water entering soil.
Percolation: Downward movement through soil/subsurface.
First Flush vs Filter
First Flush: Diverts initial runoff.
Filter: Removes suspended/physical impurities.
CGWB vs CGWA
CGWB: Central Ground Water Board.
CGWA: Central Ground Water Authority.
65. TOP 30 ONE-LINERS FOR EXAMS
Rainwater harvesting means collecting and managing rainwater.
RWH can involve storage or groundwater recharge.
Rooftop is the catchment in rooftop harvesting.
First flush diverts initial runoff.
Initial runoff may contain accumulated roof contaminants.
Recharge pits promote groundwater recharge.
Recharge trenches are elongated recharge structures.
Recharge wells facilitate recharge into suitable subsurface formations.
Percolation tanks promote infiltration and recharge.
Check dams slow runoff.
Gully plugs reduce runoff velocity and erosion.
Contour bunds conserve soil moisture.
Gabion structures can reduce runoff velocity.
Khadin is associated with Rajasthan.
Johad is associated with Rajasthan.
Kund/Tanka is associated with Rajasthan.
Guls/Kuls are associated with the Western Himalayas.
Inundation channels are associated with Bengal.
Urban paving reduces natural infiltration.
Rainwater harvesting can reduce runoff.
Rainwater harvesting can support groundwater recharge.
Improper recharge can contaminate groundwater.
Rainwater is not automatically potable after collection.
Hydrogeology is important for recharge design.
CGWB = Central Ground Water Board.
CGWA = Central Ground Water Authority.
Catch the Rain is associated with the National Water Mission.
IS 15797:2008 relates to rooftop rainwater harvesting guidelines.
1 mm rainfall over 1 m² = 1 litre.
(Q=P\times A\times C) is the basic runoff-harvesting equation.
66. MCQs — Competitive Examination Level
Q1. Rainwater harvesting primarily involves:
A. Artificial production of rainfall
B. Collection and management of rainwater
C. Desalination of seawater
D. Treatment of industrial effluents
Answer: B
Q2. Which of the following is the most appropriate sequence for rooftop rainwater harvesting?
A. Roof → Gutter → Downpipe → First Flush → Filter → Storage
B. Roof → Boiler → Turbine → Tank
C. Roof → Dam → Turbine → Filter
D. Roof → Sewer → Factory → Tank
Answer: A
Q3. The main purpose of a first-flush device is:
A. Increase rainfall
B. Divert initial contaminated runoff
C. Increase evaporation
D. Increase groundwater extraction
Answer: B
Q4. Which of the following is primarily associated with groundwater recharge?
A. Recharge pit
B. Chimney
C. Cooling tower
D. Transmission tower
Answer: A
Q5. Khadin is traditionally associated with:
A. Rajasthan
B. Assam
C. Kerala
D. Meghalaya
Answer: A
Q6. Guls/Kuls are associated with:
A. Western Himalayas
B. Thar Desert
C. Coastal Tamil Nadu
D. Deccan Plateau
Answer: A
Q7. Kund/Tanka is particularly associated with:
A. Rajasthan
B. Assam
C. Kerala
D. Goa
Answer: A
Q8. Which of the following promotes groundwater recharge?
A. Percolation tank
B. Chimney
C. Thermal plant
D. Flyover
Answer: A
Q9. CGWB stands for:
A. Central Ground Water Board
B. Central Green Water Board
C. Central Ground Weather Board
D. Central Geological Water Bureau
Answer: A
Q10. CGWA stands for:
A. Central Ground Water Authority
B. Central Green Water Authority
C. Central Ground Weather Authority
D. Central Geological Water Authority
Answer: A
Q11. One millimetre rainfall over one square metre approximately gives:
A. 0.1 litre
B. 1 litre
C. 10 litres
D. 100 litres
Answer: B
Q12. The basic equation for harvested rainwater is:
A. Q = P + A + C
B. Q = P × A × C
C. Q = P − A − C
D. Q = P/A/C
Answer: B
Q13. Which factor is especially important when selecting an artificial groundwater recharge structure?
A. Hydrogeology
B. Road traffic
C. Population language
D. Building colour
Answer: A
Q14. Urbanisation generally causes:
A. Increased natural infiltration everywhere
B. Increased impervious surfaces
C. Elimination of runoff
D. Elimination of groundwater extraction
Answer: B
Q15. Which of the following is NOT a typical objective of rainwater harvesting?
A. Groundwater recharge
B. Water conservation
C. Reduction of runoff
D. Increasing water wastage
Answer: D
67. Statement-Based Questions
Q16.
Consider the following statements:
Rainwater harvesting can be used for groundwater recharge.
Rainwater harvesting always means storage in tanks.
Rooftop rainwater can be directed towards recharge structures.
Which are correct?
A. 1 only
B. 1 and 3 only
C. 2 and 3 only
D. 1, 2 and 3
Answer: B
Q17.
Consider the following statements:
First-flush systems divert initial runoff.
Initial roof runoff can contain accumulated contaminants.
First-flush systems are designed primarily to increase evaporation.
Correct answer:
A. 1 only
B. 1 and 2 only
C. 2 and 3 only
D. 1, 2 and 3
Answer: B
Q18.
Consider the following statements:
Urban paving can reduce natural infiltration.
Rainwater harvesting can increase groundwater recharge.
Rainwater harvesting can reduce uncontrolled runoff.
Which are correct?
A. 1 only
B. 2 only
C. 1 and 2 only
D. 1, 2 and 3
Answer: D
Q19.
Consider the following statements:
Khadin is associated with Rajasthan.
Guls/Kuls are associated with the Western Himalayas.
Johad is a traditional water-harvesting system.
Which are correct?
A. 1 only
B. 1 and 2 only
C. 1, 2 and 3
D. 2 and 3 only
Answer: C
Q20.
Consider the following statements:
Filtration and disinfection are identical processes.
Rainwater collected from roofs can contain contaminants.
Potable use may require appropriate treatment and testing.
Which are correct?
A. 1 only
B. 2 and 3 only
C. 1 and 3 only
D. 1, 2 and 3
Answer: B
Q21.
Consider the following statements about groundwater recharge:
Recharge structures should be selected according to hydrogeological conditions.
Improper recharge can contaminate groundwater.
Every location is equally suitable for artificial recharge.
Which are correct?
A. 1 only
B. 1 and 2 only
C. 2 and 3 only
D. 1, 2 and 3
Answer: B
Q22.
Consider the following:
Recharge pit
Recharge trench
Recharge well
Check dam
Which of these can be associated with groundwater recharge?
A. 1 and 2 only
B. 3 and 4 only
C. 1, 2 and 3 only
D. 1, 2, 3 and 4
Answer: D
Q23.
Consider the following statements:
Rainwater harvesting can reduce surface runoff.
It can contribute to groundwater recharge.
It can completely eliminate urban flooding.
Correct answer:
A. 1 only
B. 1 and 2 only
C. 2 and 3 only
D. 1, 2 and 3
Answer: B
Q24.
Consider the following statements:
Storage and recharge are identical concepts.
Storage retains water in tanks or other storage bodies.
Recharge adds water to groundwater storage.
Correct answer:
A. 1 only
B. 2 only
C. 2 and 3 only
D. 1, 2 and 3
Answer: C
68. MATCH THE FOLLOWING
| Traditional System | Region |
|---|---|
| A. Khadin | 1. Rajasthan |
| B. Guls/Kuls | 2. Western Himalayas |
| C. Kund/Tanka | 3. Rajasthan |
| D. Inundation channels | 4. Bengal |
Correct Matching
A–1, B–2, C–3, D–4
69. FINAL EXAM REVISION MAP
RAINWATER HARVESTING
Two purposes
→ Storage
→ Groundwater recharge
Rooftop system
→ Roof
→ Gutter
→ Downpipe
→ First Flush
→ Filter
→ Storage/Recharge
Recharge structures
→ Recharge Pit
→ Recharge Trench
→ Recharge Well
→ Recharge Shaft
→ Percolation Tank
→ Check Dam
→ Dug-well Recharge
Rural structures
→ Gully Plug
→ Contour Bund
→ Gabion
→ Nala Bund
→ Check Dam
→ Percolation Tank
Traditional India
→ Khadin — Rajasthan
→ Johad — Rajasthan
→ Kund/Tanka — Rajasthan
→ Guls/Kuls — Western Himalayas
→ Inundation Channels — Bengal
Institutions
→ Ministry of Jal Shakti
→ CGWB
→ CGWA
→ National Water Mission
Campaign
→ Catch the Rain
Technical
→ (Q=P\times A\times C)
Golden numerical fact
→ 1 mm rainfall on 1 m² = 1 litre
Golden technical fact
→ Hydrogeology determines recharge suitability.
Golden safety fact
→ Filtration does not automatically mean potable water.
Golden exam fact
→ Rainwater harvesting ≠ only groundwater recharge; it can also mean storage for future use.