Explain the causes of water scarcity and stress, and evaluate supply-side and demand-side strategies for managing water resources sustainably

What this dot point is asking

SEAB wants you to explain why water scarcity and water stress arise, and to evaluate the strategies used to manage water sustainably, weighing those that increase supply against those that curb demand. The central insight is that water security is not only about how much water nature provides; it depends on demand pressures, infrastructure, governance and the environmental and energy costs of each solution, so the sustainable answer is usually an integrated portfolio rather than a single fix.

The answer

Scarcity, stress and the two kinds of shortage

Water stress is usually measured by how much of the renewable supply is being withdrawn; a country is stressed when withdrawals approach the available resource. Behind it lie two distinct causes:

• Physical water scarcity: there is genuinely not enough water relative to demand, because the climate is arid or because abstraction exceeds the rate of natural replenishment, depleting rivers and aquifers.
• Economic water scarcity: water exists physically, but people cannot access it because the storage, pipes, treatment and institutions are missing or under-funded.

The distinction matters because it points to different solutions: physical scarcity calls for diversified supply and demand cuts, while economic scarcity calls for investment in infrastructure and governance.

Why water stress is rising

Several drivers push demand up and supply down at once:

• Population and urban growth raise domestic and municipal demand.
• Rising incomes and diets increase water embedded in food, industry and energy.
• Pollution removes otherwise usable water from the pool.
• Climate change makes rainfall more variable, intensifies droughts, and (through sea-level rise) threatens coastal aquifers with saltwater intrusion.

Supply-side strategies

These increase the volume of water available:

• Reservoirs and dams store wet-season flow for the dry season, but flood land, disrupt ecosystems and trap sediment.
• Inter-basin transfers move water from surplus to deficit regions, but are costly and can harm the donor basin.
• Desalination turns seawater into freshwater and is drought-proof, but is energy-intensive and (unless powered cleanly) carbon-intensive, and produces brine.
• Wastewater reuse and recycling treat used water back to high quality, providing a weather-independent, sustainable source.

Demand-side strategies

These reduce how much water is used:

• Pricing and metering, including rising-block tariffs that charge more per unit as use rises, signal scarcity and curb waste.
• Efficiency through water-saving appliances, efficiency labelling, and industrial recycling.
• Leak reduction in the distribution network, which can recover large volumes cheaply.
• Education and conservation campaigns that shift everyday behaviour.

Demand management usually has the lowest environmental and energy cost, so it is the natural first lever, but it cannot by itself guarantee supply in a drought or for a growing city.

Examples in context

Example 1. Singapore's Four National Taps. Singapore secures water from four sources: local catchment (rainwater collected across two-thirds of the island), imported water, NEWater (treated wastewater purified to potable standard), and desalinated seawater. Diversification removes reliance on any single tap, while heavy metering, rising-block tariffs and conservation campaigns hold demand down. It is a textbook integrated strategy: maximise recycling and demand management, retain desalination for drought-proof resilience, and price water to reflect its scarcity.

Example 2. The Murray-Darling Basin, Australia. In this over-allocated basin, decades of abstraction for irrigation left rivers and wetlands degraded during drought. Management shifted toward demand-side reform: water trading, caps on extraction and buying back entitlements to return environmental flows. It illustrates economic and governance tools rebalancing an over-used system, and the difficulty of reconciling agricultural demand with ecosystem needs once physical limits are reached.

Try this

Q1. Define water stress and name two drivers that are increasing it globally. [3 marks]

• Cue. Water stress is when withdrawals approach or exceed the renewable supply available; drivers include population and urban growth, richer water-intensive diets, pollution that removes usable water, and climate change increasing variability and drought.

Q2. Explain one advantage and one drawback of desalination as a water-supply strategy. [3 marks]

• Cue. Advantage: it is drought-proof and weather-independent, turning effectively unlimited seawater into freshwater. Drawback: it is energy-intensive (and carbon-intensive unless powered cleanly) and produces concentrated brine that must be disposed of.

Q3. Explain why rising-block water tariffs are considered a sustainable demand-side strategy. [3 marks]

• Cue. Charging more per unit as consumption rises signals scarcity and rewards conservation, curbing wasteful use at low financial, energy and environmental cost, so it reduces the new supply that must be built rather than expanding abstraction.