Water supplies can be increased by using dams to control river flow, reservoirs to store water, and rainwater catchment systems to collect precipitation. They increase freshwater availability during shortages.
This is core SL and HL content in IB ESS subtopic 4.2 Water access, use and security.
How Each Strategy Works
| Strategy | Mechanism | Benefits and limitations |
|---|---|---|
| Dams | A barrier constructed across a river restricts flow and allows water to accumulate upstream. Releases can then be controlled according to demand. | Dams provide reliable water. However, they can flood habitats, interrupt sediment transport, block fish migration, and displace communities. |
| Reservoirs | Stored surface water is retained for domestic use, irrigation, industry, or release during dry periods. | Reservoirs reduce seasonal variation in supply, but water may be lost through evaporation. |
| Rainwater catchment | Rain falling on roofs or other surfaces is directed through gutters into storage tanks or local ponds. | It can reduce demand on rivers and groundwater. Supply remains dependent on rainfall, while contaminated surfaces may reduce water quality unless filtration or treatment is used. |
A common misconception is that increasing supply automatically creates water security. Water security means access to sufficient quantities of safe drinking water, so storage alone is insufficient: water quality, affordability, infrastructure, governance, and equitable distribution also matter. Large dams may benefit cities or commercial agriculture while imposing environmental and social costs on displaced or downstream communities.
For example, traditional johads in Rajasthan, India, capture monsoon runoff, recharge groundwater, and improve local dry-season supply. This illustrates how smaller-scale catchment can complement centralized infrastructure.
Exam Technique
For an explain question, link each strategy to the mechanism that increases availability. For an evaluate question, balance increased reliability against ecological impacts, economic cost, evaporation, displacement, and environmental justice, then reach a supported conclusion.