Q.Describe two general strategies used to control environmental pollution at its source (for example, in vehicle exhaust or industrial effluent), and separately describe two strategies for the preservation and protection of water resources.

Two general strategies for controlling pollution at its source: fitting vehicle exhausts with catalytic converters, which convert unburnt hydrocarbons, CO and $\text{NO}_x$ into less harmful $\text{CO}_2$, water and nitrogen before the exhaust leaves the tailpipe, and treating sewage and industrial effluent -- removing suspended solids, lowering its BOD, and neutralising toxic substances -- before it is discharged into a river or lake, rather than relying on the water body to dilute untreated waste. Two strategies for water preservation and protection: rainwater harvesting, collecting and storing rainwater or channelling it to recharge groundwater rather than letting it run off and be lost, which conserves a scarce resource; and watershed management, controlling land use across the whole catchment are …

Keep the two halves of the answer clearly separate -- pollution-control strategies first, water-preservation strat …

Blurring pollution control and water preservation together as one idea -- they are related but distinct: one reduces harmful emissions/disc …