Water Examples for IB ESS

Snow on a sunny mountain ridge can disappear without ever forming a puddle because solar radiation provides the energy for sublimation — ice changing directly into water vapour — and the same process slowly shrinks ice cubes in a closed freezer.

How it illustrates: Illustrates that solar radiation drives water movement between stores even without a liquid intermediate, addressing the misconception that sublimation is only a laboratory phenomenon.

The Mer de Glace in the French Alps (≈11.5 km long, Mont Blanc massif) demonstrates both drivers of the water cycle: solar radiation drives summer melting and high-altitude winter sublimation, while gravity drives the ice flow downhill (~75 m/year at the lower section) and the meltwater into the Arveyron, Arve and ultimately the Rhône.

How it illustrates: Shows solar radiation and gravity simultaneously driving transformations (melt/sublimation) and transfers (ice flow, streamflow) in one observable system.

Since 1850 the Mer de Glace has retreated ~2.5 km and thinned by ~200 m at Montenvers (170 m of that since 1990); the Montenvers railway station (1909) was originally next to the ice but visitors now descend a long staircase, showing that solar-driven melt and sublimation outflows now exceed snowfall inflows.

How it illustrates: Quantifies how a shift in the solar-radiation-driven energy budget changes the balance between inflows and outflows of an ice store.

Lake Geneva (Lac Léman) holds approximately 89 km³ of freshwater, which is more than half of all the surface freshwater in western Europe and provides drinking water to about 1 million people across Switzerland and France.

How it illustrates: Quantifies the surface freshwater store (0.02% of global water) by showing how a single named lake dominates an entire continental region's accessible freshwater.

Earth's water is distributed approximately as: oceans 96.5%, glaciers and ice caps 1.7%, groundwater 1.7%, surface freshwater 0.02%, atmosphere 0.001%, organisms 0.0001% — meaning less than 0.03% of all Earth's water sits in the lakes, rivers and atmosphere that humans mostly use.

How it illustrates: Quantifies the relative size of each hydrological store, illustrating how vanishingly small the accessible freshwater fraction is.

A single mature tree in the Mau Forest Complex can transpire over 200 litres of water per day through its stomata, returning water vapour directly to the atmosphere.

How it illustrates: Quantifies the transpiration flow with a deployable per-tree figure that students can scale up to explain forest-atmosphere water exchange.

At the Sondu Miriu hydropower dam in Kenya, electricity generation has been disrupted by inconsistent river flow caused by deforestation upstream in the Mau Forest, where reduced infiltration has produced lower dry-season baseflow and higher wet-season flood peaks.

How it illustrates: Demonstrates how human alteration of infiltration and transpiration upstream propagates through streamflow to undermine human infrastructure downstream.

During the 29 October 2024 Valencia DANA, the hot Mediterranean Sea (>22 °C, several degrees above the long-term October average) supplied unusually large amounts of water vapour through evaporation, which advection then fed into the stalled high-altitude low to produce >490 mm of rain in 8 hours.

How it illustrates: Shows how anthropogenic warming of an ocean store can intensify the evaporation and advection flows that drive extreme precipitation, linking human activity to altered hydrological flows.

Lake Urmia in north-western Iran lost roughly 88% of its surface area and 95% of its volume between the 1990s and 2015 after the construction of more than 50 dams and over 88,000 agricultural wells (about half illegal) diverted river streamflow and depleted groundwater for sugar beet, apple, wheat and grape irrigation, exposing a 5,000 km² salt desert that now harms ~6 million people through dust storms.

How it illustrates: Demonstrates how intensive irrigated agriculture alters flows (reduced streamflow, groundwater depletion) and shrinks a major surface freshwater store.

On 29 October 2024 a DANA dropped over 490 mm of rain in 8 hours on the Valencia region of Spain; sealed urban surfaces, cleared orchards and the unprotected barranco del Poyo (peak discharge ~2,300 m³/s) turned the rainfall into a flash flood that killed over 230 people, the deadliest in modern Spanish history.

How it illustrates: Shows how urbanisation reduces infiltration and evapotranspiration while sharply increasing surface run-off and streamflow peaks, amplifying flood risk.

Since the 1990s about 25% of Kenya's Mau Forest Complex (over 100,000 hectares) has been cleared for subsistence agriculture, tea, charcoal and settlement; transpiration (a mature tree transpires >200 L/day) and interception have collapsed, infiltration has fallen and the Mara River now suffers near-dry dry seasons and higher wet-season flood peaks, threatening the Maasai Mara–Serengeti migration and Sondu Miriu hydropower.

How it illustrates: Demonstrates how deforestation alters multiple flows (transpiration, interception, infiltration, run-off) and degrades groundwater and streamflow stores.

The Mau Forest Complex in western Kenya is the source of 12 major rivers including the Mara, Sondu, Njoro and Ewaso Ng'iro, which feed Lake Victoria (and the Nile), Lake Nakuru, Lake Natron and the Maasai Mara–Serengeti ecosystem, earning it the title of Kenya's most important 'water tower'.

How it illustrates: Demonstrates the regional-scale dependence of multiple hydrological stores and streamflows on a single forested catchment, framing why deforestation here has cascading water-cycle consequences.

By the 2010s the number of agricultural wells in the Lake Urmia catchment had risen to over 88,000 (around half of them illegal), depleting the groundwater store faster than it could recharge and contributing to the lake losing 88% of its surface area by 2015.

How it illustrates: Quantifies how agricultural abstraction can simultaneously deplete the groundwater store and starve a surface freshwater store of streamflow inputs.

During the 29 October 2024 Valencia floods, the barranco del Poyo went from no flow to a peak discharge of around 2,300 m³/s in less than two hours — comparable to the average flow of the Rhône at Lyon — as sealed urban surfaces converted rainfall directly into surface run-off.

How it illustrates: Quantifies how urbanisation collapses infiltration and amplifies streamflow into a flash-flood pulse, giving a concrete discharge figure students can deploy.

Since 2013 the Urmia Lake Restoration Programme has attempted to reduce agricultural water use by 40%, switch to less thirsty crops, release water from upstream dams and trial cloud seeding; the lake has partially recovered in some years but remains far below its 1990s extent.

How it illustrates: Demonstrates a government attempt to reverse human-induced changes to hydrological flows and restore a shrunken store.

Spain's Plan Sur diversion canal, built around Valencia after the catastrophic 1957 Túria flood, protected the city centre in October 2024 but the southern suburbs along the unprotected barranco del Poyo were devastated, illustrating how engineered changes to streamflow routing only redistribute, not eliminate, flood risk in urbanised catchments.

How it illustrates: Shows a specific human engineering intervention that altered streamflow pathways to manage flood risk in an urbanised catchment.

A hypothetical scenario for Lake Geneva in which climate change reduces Rhône inflow by 20% (losing 1.14 km³/yr) and increases evaporation by 50% (losing 0.2 km³/yr) would shift the lake from steady state to an annual deficit of ~1.34 km³/yr, demonstrating how small percentage changes to individual flows break the input–output balance.

How it illustrates: Shows how flow diagrams of inputs and outputs can be used quantitatively to test whether a named water body remains in steady state under changing conditions.

Lake Geneva (Lac Léman, ~89 km³) is approximately in steady state with annual inputs ≈ outputs ≈ 7.1 km³/year: Rhône inflow 5.7, other tributaries 0.7, direct precipitation 0.6 and groundwater 0.1 km³/year balance Rhône outflow 6.6, evaporation 0.4 and drinking-water abstraction 0.1 km³/year supplying ~1 million people.

How it illustrates: Provides a fully quantified input/output flow diagram showing how a lake's steady state is demonstrated through balanced budgets.

The Salar de Atacama freshwater aquifer in northern Chile has annual recharge of 180 million m³/year against natural seepage (120), evaporation (30) and town abstraction (15), leaving only 15 million m³/year of headroom before steady state is breached — relevant because the salar holds the world's largest lithium reserves and mining companies have requested an additional 40 million m³/year.

How it illustrates: Shows how a steady-state water budget is used to calculate the maximum sustainable abstraction from an aquifer under competing demands.

The WHO estimates that a person needs around 20 litres per day as an absolute minimum for drinking, cooking and basic hygiene, and 50–100 litres per day for a comfortable standard of living.

How it illustrates: Quantifies the 'sufficient amount' component of water security, giving students a deployable numerical threshold.

During Cape Town's 'Day Zero' crisis (2015–2018), the city's six main dams fell to around 23% capacity, the per-person limit was cut to 50 L/day in February 2018, and farmers' irrigation allocations were cut by 60%; wealthy residents drilled private boreholes while informal settlement residents (~20% of the city) shared communal taps, exposing apartheid-era infrastructure inequalities.

How it illustrates: Demonstrates how social, cultural, economic and political factors simultaneously shape unequal access to freshwater within a single city.

The legacy of apartheid (ended 1994) shaped Cape Town's 2018 water crisis: infrastructure had historically been built to serve white suburbs, while townships and informal settlements remained under-served, so during Day Zero the poor relied on shared communal taps while wealthy households drilled private boreholes.

How it illustrates: Illustrates how historical political decisions create lasting inequalities in freshwater access between groups within the same city.

Comparison data (World Bank/WHO–UNICEF JMP, 2022–23): Switzerland (~1,200 mm rainfall, GDP/capita ~US$95,000) and the UAE (~100 mm rainfall, ~US$50,000) both have ~99–100% safely managed drinking water, while Haiti (~1,400 mm, ~US$1,700) and Niger (~150 mm, ~US$600) sit at ~23% and ~14%.

How it illustrates: Shows that economic and political capacity, not rainfall, determines equitable access to safe freshwater across countries.

Globally, agriculture accounts for roughly 70% of freshwater withdrawals, industry for ~20% and domestic use for ~10%, with population growth and rising per-capita consumption (showers, washing machines, meat-heavy diets) identified as more important drivers of water stress than climate change in many regions.

How it illustrates: Quantifies the sectoral split of demand and identifies the mechanisms by which population growth and economic development increase water use.

Cape Town used steeply rising block tariffs during its 2017–18 drought — cheap for the first 6 kL per household per month, then progressively more expensive — to protect basic use while penalising heavy users and encourage greater efficiency.

How it illustrates: Demonstrates a demand-side policy response (improving efficiency of utilisation) to growing water demand under scarcity.

Rather than build a US$8–10 billion filtration plant, New York City chose to protect its Catskill/Delaware watershed 200 km upstream, spending over US$1.5 billion on land purchases, farmer payments and stream restoration to protect more than 140,000 acres (~57,000 ha), delivering near-unfiltered water to ~9.5 million people.

How it illustrates: Demonstrates enhancement of natural wetlands/watersheds as a cost-effective ecosystem-services approach to securing urban water supply.

The Dar Si Hmad fog harvesting project at Mount Boutmezguida in the Aït Baamrane region of southern Morocco uses ~1,700 m² of mesh nets to collect on average ~35,000 litres of water per day during the June–November fog season, supplying 16 villages and more than 1,000 people, and cutting women's daily water-collection time from ~3 hours to almost zero.

How it illustrates: Demonstrates rainwater/fog catchment as a low-energy, village-scale supply enhancement with strong social benefits but limited by geography.

The Grand Ethiopian Renaissance Dam (GERD) on the Blue Nile, inaugurated September 2025, has a reservoir capacity of ~74 km³ and generates ~5,150 MW of hydropower at a cost of ~US$5 billion, but displaced 5,000–20,000 people and is fiercely opposed by Egypt, which depends on the Nile for ~97% of its freshwater.

How it illustrates: Shows how dams and reservoirs can massively boost water and energy supply but create transboundary conflict and ecological/social costs.

The United Arab Emirates obtains around 42% of its water from desalination and produces ~14% of the world's desalinated water; the Jebel Ali plant in Dubai produces over 2 billion L/day and the Taweelah RO plant in Abu Dhabi (commissioned 2022) ~909,000 m³/day, but ~66% of the energy still comes from fossil fuels and brine discharge harms coastal ecosystems.

How it illustrates: Shows desalination (especially reverse osmosis) as a major supply-enhancement strategy for arid states, including its energy and ecological costs.

Haiti is a classic example of economic water scarcity: despite ~1,400 mm of annual rainfall, around 70% of the population lacks safely managed drinking water and two-thirds lack basic sanitation, because political instability and disasters like the 2010 earthquake have left treatment plants and pipes underbuilt.

How it illustrates: Shows economic scarcity — water is physically abundant but cannot be delivered safely due to lack of infrastructure and governance.

Jordan is a clear example of physical water scarcity: in 2021 each Jordanian had only around 61 m³ of renewable freshwater per year, far below the absolute scarcity threshold of 500 m³, and about half of households receive piped water only once a week despite extensive infrastructure.

How it illustrates: Demonstrates physical scarcity where climate and geography limit the actual abundance of water regardless of infrastructure.

Melbourne's Stage 3a restrictions (April 2007 – April 2010) banned daytime watering and most lawn watering during the Millennium Drought, helping cut per-capita household consumption from ~458 L/day in 1996 to ~236 L/day in 2011.

How it illustrates: Quantifies how domestic rationing nearly halved household water use over a sustained drought.

Sydney Water installed 7,500 smart meters across four pilot suburbs in 2023, with trial households cutting consumption by 7–10%; the scheme is being rolled out to 1.6 million properties across Greater Sydney.

How it illustrates: Quantifies the demand-reduction impact of domestic metering technology.

The dual-flush toilet was invented in Australia in 1980 by Caroma, and since 1993 all new toilets sold in Australia must be dual-flush, saving an estimated 32,000 L per household per year.

How it illustrates: Shows how a low-flush toilet policy combined with technology innovation delivers measurable domestic water savings.

Chennai's 'Day Zero' arrived in June 2019 when all four city reservoirs ran dry, forcing families to queue for just 25 L of water per day.

How it illustrates: Shows extreme domestic rationing imposed by scarcity in a megacity.

Delhi provides the first 20,000 L per household per month free and only meters above that threshold, which weakens the incentive for low-volume households to save water.

How it illustrates: Counter-example showing how poorly designed metering tariffs can undermine domestic conservation incentives.

Since 2016 Bengaluru has required new apartment complexes with 20+ flats to install on-site sewage and grey-water treatment with dual piping so treated water is reused for flushing and gardens.

How it illustrates: Demonstrates regulatory mandating of domestic grey-water recycling in new urban housing.

Tamil Nadu made rainwater harvesting compulsory for all buildings in 2003; around 5 million homes were retrofitted within three years and Chennai's groundwater table rose by up to 50% in some areas.

How it illustrates: Quantifies the aquifer recharge benefits of mandatory domestic rainwater harvesting.

Under the NSW BASIX scheme, all new homes built in New South Wales since 2004 must meet water-saving targets, most commonly via a rainwater tank; around 26% of Australian households now have a tank, rising to ~50% in Adelaide.

How it illustrates: Demonstrates regulation-led mandatory rainwater harvesting at domestic scale.

A$13 billion of Australian federal investment since 2012 has converted Murray-Darling Basin farms from flood to drip and sprinkler irrigation, saving an estimated 700 GL per year by 2024.

How it illustrates: Quantifies the scale of water savings from a national drip-irrigation conversion programme.

FarmRak on Queensland's Sunshine Coast runs a closed-loop aquaponics farm pairing barramundi with herbs and vegetables for Brisbane restaurants, using around 90% less water than soil farming.

How it illustrates: Illustrates commercial aquaponics achieving the syllabus-cited ~90% water reduction.

India championed the UN International Year of Millets in 2023; pearl millet (bajra), ragi and sorghum grow with rainfall as low as 350 mm/year (versus ~1,200 mm for rice), and government schemes expanded millet area to 13.7 million ha by 2024.

How it illustrates: Quantifies how promoting drought-resistant crops cuts irrigation demand at national scale.

Madhavi Farms in Karnataka, India operates a commercial 100,000 L aquaponics system producing 6 tonnes of fish and 50 tonnes of vegetables per year, with urban rooftop systems also spreading in Bengaluru and Hyderabad.

How it illustrates: Shows aquaponics applied at commercial scale in a middle-income context.

Sundrop Farms in Port Augusta, South Australia uses a 20 ha greenhouse with solar-desalinated seawater to grow ~17,000 tonnes of tomatoes per year using no fresh water and no fossil fuels; built for around A$200 million.

How it illustrates: Showcases a high-capital greenhouse strategy that eliminates freshwater use in industrial food production.

Around 30–40% of Indians identify as vegetarian (the largest absolute number in the world) based on culture and religion, contributing to an average Indian water footprint of ~980 m³ per capita per year against ~2,840 m³ in the United States.

How it illustrates: Quantifies how widespread vegetarian food production reduces national water footprint.

Producing 1 kg of beef requires around 15,000 L of water, compared with ~1,800 L for 1 kg of wheat and ~4,000 L for 1 kg of pulses, demonstrating the water savings from switching toward vegetarian food production.

How it illustrates: Quantifies the water-footprint gap that underpins the dietary-shift conservation strategy.

India's Pradhan Mantri Krishi Sinchayee Yojana (PMKSY) scheme, launched 2015, had put around 8 million ha under drip and sprinkler systems by 2024, with federal subsidies covering 45–55% of costs.

How it illustrates: Demonstrates subsidy-led national rollout of drip irrigation as an industrial water-conservation strategy.

Polyhouse cultivation in India expanded under the Mission for Integrated Development of Horticulture to about 56,000 ha by 2023, pairing drip irrigation with rainwater collection from greenhouse roofs and 50–75% government subsidies.

How it illustrates: Shows subsidy-driven scaling of rainwater-recycling greenhouses for industrial food production.

CSIRO and the University of Adelaide developed a salt-tolerant durum wheat using a salt-tolerance gene, yielding 25% more in saline soils, with successful trials in the Western Australia wheat belt 2018–2024.

How it illustrates: Demonstrates breeding of drought/salinity-resistant crops to reduce irrigation demand.

In March 2024 Bengaluru, India (population ~13 million) ran dry across whole districts after the Cauvery River shortage and failing groundwater forced families to queue for hours at private water tankers, prompting bans on using drinking water for car washes, gardens, fountains and construction with fines up to ₹5,000.

How it illustrates: Demonstrates a named country's mitigation response (rationing + metering tightening) to an acute water scarcity event.

Sydney's Warragamba Dam, which supplies about 80% of the city's water, fell below 45% in December 2019 — its lowest since the Millennium Drought — triggering Level 2 restrictions banning hose use outside set hours.

How it illustrates: Shows an Australian mitigation response combining infrastructure monitoring with domestic rationing during scarcity.

Agriculture accounts for around 70% of global freshwater withdrawals while domestic use is only ~12%, meaning national mitigation strategies must combine industrial and household measures to address scarcity.

How it illustrates: Frames why named-country mitigation strategies must integrate both 4.2.6 and 4.2.7 measures.