The world is facing an acute shortage of clean and safe alternative freshwater. What are the technologies which can solve this crisis? Briefly discuss any three such technologies, citing their key merits and demerits.

Desalination

Reverse osmosis (and, less often now, thermal distillation) turns seawater or brackish water into potable or industrial water. Merit: it is climate-independent at the coast and can supply a city that has no river left. Gulf States and some Indian coastal plants already run on this logic. Demerit: it is energy-heavy, which means a carbon bill unless the plant is paired with clean power. Brine returned to the sea can harm local ecology. Capital cost is high, so the water is often too dear for irrigation. Inland, there is no sea to draw.

• Peg: Coastal RO is the mature large-scale option; brine and power are the constraints that never leave.
• Peg: Brackish-groundwater RO is a cousin used in some Indian inland belts, with a concentrate-disposal problem.

Wastewater reuse

Treating municipal and industrial sewage to a standard that allows industrial cooling, horticulture, or, with higher treatment, potable reuse creates a new river inside the city. Merit: it cuts both pollution and fresh abstraction; the source is located where the demand is. Singapore’s reused-water story is the global teaching case; several Indian cities now mandate treated reuse for industry and parks. Demerit: public distrust of toilet-to-tap, patchy sewage collection, and plants that are built and not run. If the sewer never reaches the plant, the technology is a shed.

• Peg: Tertiary treatment plus dual plumbing or industrial offtake is the practical Indian path; direct potable reuse is rarer.
• Peg: A dry STP is not a technology failure; it is an O&M failure.

Managed aquifer recharge and rainwater harvesting

Check dams, percolation tanks, recharge wells and rooftop harvesting put monsoon water back into soil and aquifers instead of into a flood drain. Merit: low energy, local, and suited to India’s monsoon pulse. It treats the aquifer as a reservoir. Demerit: it cannot create water in a drought year if there is no rain to harvest. Poorly designed recharge can push polluted runoff into drinking aquifers. It does not, by itself, supply a megacity’s 24×7 pressurised network.

• Peg: Atal Bhujal-style community recharge and city rainwater by-laws are the Indian policy face of this technology.
• Peg: Three technologies, three scales: coast, city sewage, and monsoon land. None is a solitary saviour.