Part 1 of 2
Sources of Water & Intake Structures
Last reviewed 16 Sept 2026 · 7 min read
Sources of water
Water sources are broadly surface or subsurface (groundwater) sources.
Surface sources
| Source | Quantity | Quality |
|---|---|---|
| Rivers and streams | Large in perennial rivers; flows fluctuate — minimum (lean season) flow governs reliability | Turbid in floods; exposed to pollution from towns and industries upstream; needs full treatment |
| Natural lakes and ponds | Depends on catchment and storage; usually reliable for small towns | Less turbidity (settling), but algae, tastes and odours; eutrophication risk |
| Impounding reservoirs (dams) | Large, regulated supply — stores monsoon flows for dry seasons | Clearer water due to settling; stratification in deep reservoirs; algae; quality varies with depth (so multi-level intakes) |
| Canals | Depends on canal operation (closures) | Similar to river water, with contamination risk along the route |
Subsurface sources
| Source | Features |
|---|---|
| Springs | Natural outflow of groundwater; gravity springs (water table cuts the ground surface), surface springs, artesian springs; supply for hill towns |
| Infiltration galleries | Horizontal perforated conduits laid in sand/gravel along or under river beds; collect naturally filtered water |
| Infiltration wells | Shallow wells sunk in river beds, connected to a jack well |
| Open (dug) wells | Shallow unconfined aquifers; small supplies |
| Tube wells | Deep aquifers; large yields; common source for towns and rural schemes |
Groundwater is generally clear, free of pathogens and cooler, but may be hard or contain iron, fluoride, arsenic, nitrate or salinity; quantity is limited by aquifer recharge.
Alternative sources
- Rainwater harvesting — rooftop and surface runoff collection for storage or recharge.
- Desalination of sea or brackish water (reverse osmosis, multi-stage flash distillation) — energy-intensive; used in some coastal cities.
- Reuse of treated wastewater for non-potable uses (industry, gardening, flushing).
Selection of a source
- Quantity — adequate for the design period, including in droughts.
- Quality — minimum treatment required; free from pollution risk.
- Distance and elevation — nearer and higher sources reduce conveyance and pumping cost (gravity supply preferred).
- Cost — capital and operation and maintenance.
- Reliability and legal rights — water rights, inter-state issues.
Intake structures
An intake is a structure placed in or near a source to withdraw water and discharge it into the conveyance system (intake conduit, jack well, pumping main). It is usually a masonry or concrete structure with openings fitted with screens.
Types
| Type | Description |
|---|---|
| River intake | Circular masonry tower (intake well) in or near the river with ports at different levels; water flows through screens into the well and is pumped out |
| Reservoir intake | Tower near the dam (often part of it) with inlets at several levels so the best-quality water can be drawn as the level changes; access by a foot bridge |
| Lake intake | Pipe or conduit laid in the lake bed with a bell-mouth entry protected by a crib or screen; conveys water to a shore sump |
| Canal intake | Masonry chamber on the canal bank with a screened inlet pipe |
| Submerged intake | Entirely under water (a crib of timber/concrete with pipe entry); cheap, does not obstruct navigation, but hard to inspect and clean |
| Exposed intake | Tower above water level; accessible for maintenance and operation of gates |
| Wet intake tower | Water enters the tower well (water level inside ≈ source level) and then flows into the conduit through gates |
| Dry intake tower | Inlet pipes lead directly to the conduit; the tower is dry inside; water can be drawn from any level independently; tower must be designed for buoyancy/uplift |
Site selection for intakes
- Located upstream of towns and sewage or industrial outfalls, where water is purest.
- Adequate depth of water at the lowest level (entry below the lowest water level) — preferably on a straight stable reach or the concave (deep) side of a bend.
- Good foundations and safety against scour, floods, floating debris and ice.
- Not in navigation channels; easy access.
- Should not be where heavy currents or rapids cause damage; avoid sites with sand bars forming.
- Close to the treatment plant and supply area where possible, and able to accommodate future expansion.
Design considerations
- Screens: coarse screens (bars) at the entry to exclude large floating matter, and fine screens for smaller debris; cleaned manually or mechanically.
- Low entrance velocity through the ports (commonly well below about 0.6 m/s) to avoid drawing in debris, sediment and fish.
- Inlets at multiple levels (reservoir and river intakes) — withdraw clearer water as levels and quality vary.
- Stability against water pressure, wave and ice forces, buoyancy (dry towers), scour.
- Capacity for the maximum daily demand at the end of the design period (intake structures commonly designed for about 30 years).
- Provision for isolation (gates/valves) and cleaning.
Conveyance of raw water
- Gravity (free-flow) conduits — canals, aqueducts, flumes, tunnels, grade aqueducts; follow the hydraulic gradient; cheap where terrain permits.
- Pressure conduits — pipelines (mild steel, ductile iron, prestressed concrete, GRP, HDPE) that can follow ground undulations below the hydraulic gradient line.
- Pumping from a jack well/sump at the intake through a rising main to the treatment plant; pumps designed for maximum daily flow with standby units.
FormulaPumping power
= total head = static lift + friction and minor losses; = overall efficiency of the pump set.
Economical diameter of a rising main is found by balancing pipe capital cost (increases with diameter) and pumping energy cost (decreases with diameter); velocities of roughly 1–2 m/s are commonly economical.