Last reviewed 16 Sept 2026 · 8 min read
Natural recharge
Groundwater recharge is the addition of water to the zone of saturation. Natural sources:
- Infiltration of rainfall (the major source).
- Seepage from rivers, canals, tanks and reservoirs (influent streams).
- Return flow from irrigation.
- Inflow from adjoining aquifers.
Estimating recharge
= specific yield; = area; = rise in water table during the recharge season; = gross groundwater draft during the same period (plus other losses as applicable).
- Rainfall infiltration factor method — recharge = a norm (fraction of rainfall) depending on soil/rock type; used where water-level data are inadequate.
- Tracer and soil-moisture balance methods.
In India, the Groundwater Estimation Committee (GEC) methodology (revised 2015) is used by the Central and State Groundwater Boards for periodic assessments.
| Stage of extraction | Category |
|---|---|
| ≤ 70% | Safe |
| > 70% and ≤ 90% | Semi-critical |
| > 90% and ≤ 100% | Critical |
| > 100% | Over-exploited |
Long-term water-level trends are also checked when assigning categories. Separately, units with poor groundwater quality are flagged as saline.
Artificial recharge
Artificial recharge augments groundwater by deliberately increasing infiltration or injecting water.
| Method | Description | Suitable where |
|---|---|---|
| Spreading basins / flooding | Water spread over large flat areas or in shallow basins | Permeable soils, surplus surface water available |
| Ditches and furrows | Shallow flat-bottomed channels close together | Irregular terrain |
| Percolation tanks | Small reservoirs on streams built mainly to percolate water (not for irrigation) | Moderately permeable strata, hard-rock areas with weathered zones |
| Check dams / nala bunds / gabion structures | Small barriers across streams to hold water and increase percolation | Hilly and rocky terrain |
| Recharge pits and trenches | Excavations filled with boulders, gravel and coarse sand | Thin impervious surface layer over permeable strata |
| Recharge shafts | Deeper shafts piercing low-permeability layers | Clay cap overlying aquifer |
| Injection (recharge) wells | Water pumped/poured into a well tapping a confined aquifer | Deep confined aquifers; urban areas; needs treated water to avoid clogging |
| Dug well recharge | Filtered runoff diverted into existing or defunct open wells | Alluvial and hard-rock areas |
| Induced recharge | Pumping wells near rivers draw water from the stream into the aquifer | Rivers hydraulically connected to aquifers |
| Subsurface dykes (groundwater dams) | Impermeable barrier across a sub-surface channel to hold groundwater | Narrow valleys with shallow bedrock |
Clogging by suspended silt, algae and bacteria is the main operational problem — pre-treatment (desilting chambers, filters), periodic scraping and drying cycles are needed.
Rooftop rainwater harvesting
Components: roof catchment, gutters and downpipes, first-flush diverter, filter (sand–gravel or mesh), storage tank or recharge structure (pit, trench, borewell). Runoff coefficients are high for hard roofs (commonly about 0.75–0.95) and low for thatch.
Conjunctive use
Planned, coordinated use of surface water and groundwater — e.g. canal water in wet seasons and groundwater pumping in dry seasons. Benefits: controls waterlogging in canal commands, reduces groundwater depletion elsewhere, uses aquifer storage (no evaporation loss), improves reliability.
Groundwater quality
Groundwater is generally free of suspended matter and pathogens but may carry dissolved minerals from the rocks it passes through.
Key contaminants and drinking water limits (IS 10500:2012)
| Parameter | Acceptable limit | Permissible limit (no alternate source) | Health effect |
|---|---|---|---|
| Total dissolved solids | 500 mg/L | 2000 mg/L | Taste, laxative effects |
| Fluoride | 1.0 mg/L | 1.5 mg/L | Dental and skeletal fluorosis above limit; dental caries if very low |
| Arsenic | 0.01 mg/L | No relaxation | Skin lesions, cancer (arsenicosis) — notable in parts of the Ganga–Brahmaputra plains |
| Nitrate | 45 mg/L (as NO₃) | No relaxation | Methaemoglobinaemia (blue baby syndrome) |
| Total hardness (as CaCO₃) | 200 mg/L | 600 mg/L | Scale, soap wastage |
Other concerns: iron and manganese (taste, staining), salinity, uranium in some granitic areas, microbial contamination from septic tanks.
Sources of groundwater pollution
Septic tanks and leaking sewers; landfills and dumps (leachate); fertilisers and pesticides (nitrate); industrial effluents injected or discharged on land; mining; over-pumping in coastal areas (salinity); geogenic sources (fluoride, arsenic).
Pollution is persistent because groundwater moves slowly and has little dilution or aeration — prevention is far easier than remediation (pump-and-treat, permeable reactive barriers, bioremediation).
Sea-water intrusion
In coastal aquifers, lighter fresh water floats above denser sea water. Excessive pumping lowers the fresh-water head and the salt-water wedge moves inland.
Depth of the fresh–salt interface below mean sea level:
With = 1.025 and = 1.000: , where = height of the water table above mean sea level.
So lowering the water table by 1 m raises the interface by about 40 m.
Control: reduce and redistribute pumping; artificial recharge; injection barriers (line of recharge wells parallel to the coast); extraction barriers (pumping wells to intercept salt water); subsurface physical barriers; relocating wells inland.