CHAPTER 5

Sources of Water — Surface and Groundwater

Water Sources

Describes surface water sources (rivers, lakes, reservoirs, canals), groundwater sources (tube wells, open wells, springs), and rainwater harvesting. Covers yield estimation, sustainability assessment, seasonal variations, and source selection criteria.

🏞 Sources & IntakeManual on Water Supply and Treatment3rd Edition (1999) with 2024 revision updates

Key formulas

Safe Yield (rivers, from FDC): Q_95 = flow equaled or exceeded 95% of days in a year — typical design basis for river abstraction.
Well yield (specific capacity): Q/s = well discharge / drawdown (m³/hr/m) — measure during pumping test.
Groundwater safe yield: annual recharge × 0.7 (factor of safety for drought years).
Rainwater harvesting potential: V (m³) = A (m²) × R (m) × C, where A = roof area, R = annual rainfall in m, C = runoff coefficient (0.75-0.90 for paved roofs).

Key values & thresholds

river abstraction design basis: Q_95 (95% dependable flow)
reservoir storage months: 6-12 (dry period)
tube well typical yield m3 per hr: 15-100
dug well typical yield m3 per hr: 5-25
spring yield m3 per day range: 10-500
groundwater safe yield factor: 0.7 of annual recharge
rainwater runoff coefficient paved: 0.75 - 0.90
rainwater runoff coefficient paved rural: 0.60 - 0.75
well drawdown max m: 1/3 of water column

Clause-level requirements

Source selection priority: surface (if available, most reliable) > groundwater (confined > unconfined) > rainwater harvesting > seawater desalination (coastal) > wastewater reuse.
River abstraction design: base on Q_95 (flow exceeded 95% of the year) for continuous supply. For seasonal rivers, provide reservoir storage for dry period.
Groundwater abstraction: limit to 70% of annual recharge to ensure sustainability. Deep confined aquifers preferred for long-term reliability.
Dug wells: yield 5-25 m³/hr from shallow water table; suitable for villages. Tube wells: 15-100 m³/hr from deeper aquifers; urban and rural use.
Rainwater harvesting: supplements other sources; from roofs (cleaner) or ground (requires filtration). Annual potential = roof area × rainfall × runoff coefficient.
Source water quality pre-screening: chemical (TDS, hardness, fluoride, arsenic, nitrate), bacteriological (fecal contamination), physical (turbidity, color, odor). Unsuitable sources excluded.

Practitioner notes — what goes wrong in the field

Indian urban supply: ~60% from surface water (Ganga, Yamuna, Krishna, Cauvery, Narmada etc.), 30% from groundwater, 10% rainwater/desalination/recycled.
Delhi draws 80% of water from Yamuna + Ganga via canal; Mumbai from 6 lakes (Vihar, Tulsi, Tansa, Bhatsa, Modak Sagar, Upper Vaitarna); Chennai from reservoirs and Krishna water via Telugu Ganga canal.
Groundwater depletion is severe — Gurgaon, Bengaluru outskirts, Rajasthan have water tables dropping 1-3 m/year. Restrict new tube well permissions; mandatory rainwater harvesting.
Tube well design: borehole depth 50-250 m typical; screen in productive aquifer zone; annular space gravel-packed and sealed to prevent surface contamination.
Well yield test (pumping test): minimum 72 hours constant-rate pumping with drawdown recording. Results determine sustainable yield.
Arsenic-contaminated shallow aquifers (West Bengal, Bihar): switch to deeper confined aquifers (150-300 m) which are typically arsenic-free.
Fluoride-contaminated zones (Rajasthan, Gujarat, Karnataka): blend with low-fluoride sources or provide defluoridation at community or household level.
Desalination for coastal cities: Chennai (Nemmeli 100 MLD), Jamnagar, Minjur — RO plants. Cost ₹30-60 per m³ (3-5× conventional).
Recycled wastewater: used for non-potable (toilet flushing, gardening, cooling) — Bangalore, Pune, Delhi pilot projects. IS 10500 standards apply if potable use.
Spring sources (Uttarakhand, Himachal, NE states): protect from contamination with chamber, chlorinate, measure yield seasonally (reduces in dry months).
Rainwater harvesting: mandatory in Bangalore, Chennai, Delhi for buildings > 100 m² roof area. Typical 100 m² roof in 800 mm rainfall area yields 60-70 m³/year.

FAQs

What is Q_95 for river abstraction design?

Q_95 = flow equaled or exceeded 95% of days in a year. Design basis for continuous river water abstraction. Calculated from Flow Duration Curve using 10-30 years of daily discharge data.

What is safe yield of groundwater?

70% of annual recharge to ensure sustainability. Overpumping (> annual recharge) leads to water table decline, land subsidence, aquifer salinization. Central Ground Water Board (CGWB) classifies blocks: Safe / Semi-Critical / Critical / Over-exploited.

How much water can a tube well yield?

Typical 15-100 m³/hr depending on aquifer productivity and well design. Yield measured via pumping test (72-hour constant rate). Specific capacity (Q/s) = discharge/drawdown indicates aquifer performance.

What is rainwater harvesting potential formula?

V (m³) = A (m²) × R (m) × C, where A = catchment (roof) area, R = annual rainfall in meters, C = runoff coefficient (0.75-0.90 for paved roofs). Example: 100 m² × 0.8 m × 0.85 = 68 m³/year.

Which source is most reliable?

Priority: surface water with adequate storage (most reliable, quality good) > confined groundwater (reliable, quality usually good) > unconfined groundwater (seasonal variation, contamination risk) > rainwater (seasonal) > desalination (expensive but drought-proof) > recycled water (non-potable mainly).

Cross-references

CGWBCWCIS 2800 Well ConstructionIS 8605 Water SourcesCPHEEO WS Chapter 4