🎒 Base knowledge and understanding

🌿 Content

🔑 Key terms

Phase 1: Two cities, same problem

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Bengaluru, India, March 2024

"Bengaluru runs dry: tankers queue as groundwater wells fail"

India's tech capital, with around 13 million people, ran out of water across whole districts. The Cauvery River shortage and failing groundwater forced households to depend on private water tankers, with families queuing for hours.

https://maps.app.goo.gl/XEvSzViAFq7vQQVE8

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Sydney, Australia, December 2019

"Warragamba Dam below 45%"

The dam that supplies around 80% of Sydney's water dropped to its lowest level since the Millennium Drought. Level 2 water restrictions banned hose use outside set hours, and Sydneysiders were urged to cut indoor use too.

https://maps.app.goo.gl/tnqCwdL5kd2MarGQ9

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Discuss in pairs

  1. What are two things these cities have in common?

  2. Both have access to the same five domestic conservation techniques and the same five industrial strategies. Why might they use them very differently?

By the end of this lesson you will know what those techniques are, and you will be able to outline how each country combines them into a national response to scarcity.

Phase 2: Domestic conservation

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4.2.6 Water conservation techniques can be applied at a domestic level.

Include techniques such as metering, rationing, grey-water recycling, low-flush toilets, rainwater harvesting.

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The five techniques

Domestic water use is only around 12% of global water consumption, but it is the most visible part of water use and the gateway to behaviour change. The IB syllabus lists five techniques that householders or governments can use to reduce domestic demand.

  1. Metering: devices that measure household water use, so consumers can see what they consume and (usually) pay for it. Studies show metered households use 15 to 30% less water than unmetered ones.

  2. Rationing: official restrictions on when, how or for what purpose water can be used, often imposed during droughts.

  3. Grey-water recycling: capturing lightly used water from showers, sinks and laundry to reuse for flushing toilets or watering gardens. Can cut household demand by 30 to 50%.

  4. Low-flush toilets: toilets using 4 to 6 L per flush instead of the 11 to 20 L of older models. Toilets account for around a quarter of household water use.

  5. Rainwater harvesting: collecting rainfall from roofs into tanks for non-potable use (gardens, flushing, washing).

  6. Why does the IB consider domestic conservation important even though it accounts for only 12% of global water?

  7. Which two of the five techniques rely on changing user behaviour rather than installing technology?

  8. Which two of the five techniques would be most useful in a city that already has piped water but suffers frequent drought?

Compare: Australia and India

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Australia: high-income, regulation-led

Metering: Almost 100% of Australian urban homes are metered, with volumetric pricing (the more you use, the more you pay). Sydney Water installed 7,500 smart meters across four pilot suburbs in 2023; trial households cut consumption by 7 to 10%. The plan is to roll out 1.6 million across Greater Sydney.

Rationing: Melbourne's Stage 3a restrictions, in force from April 2007 to April 2010, banned daytime watering and most lawn watering. Per-capita household consumption nearly halved across the Millennium Drought, from around 458 L per day in 1996 to 236 L per day in 2011. Sydney imposed Level 2 restrictions in December 2019.

Grey-water recycling: Several Australian states have offered rebates for households installing grey-water diverters, which redirect shower and laundry water away from sewers. Untreated grey water can legally be used for underground garden pipes.

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

Rainwater harvesting: Under the NSW BASIX scheme, all new homes since 2004 must meet water-saving targets, most commonly achieved by installing a rainwater tank. Around 26% of Australian households now have a tank, rising to about 50% in Adelaide.

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India: middle-income, mixed approach

Metering: Bengaluru tightened volumetric metering and pricing after the Cauvery shortage of March 2024 and reported significant consumption cuts in piloted zones. Delhi provides the first 20,000 L per household per month free, then meters above that, which weakens the incentive to save below the threshold.

Rationing: Chennai's "Day Zero" came in June 2019 when all four reservoirs ran dry, with families queuing for 25 L per day. Bengaluru in March 2024 banned drinking water for car washes, gardens, fountains and construction; fines reached ₹5,000 (about £45).

Grey-water recycling: Since 2016, Bengaluru has required new apartment complexes with 20 or more flats to install on-site sewage and grey-water treatment, plus dual piping so the treated water is reused for flushing and gardens. Chennai now mandates dual plumbing in many new buildings.

Low-flush toilets: India's National Building Code 2016 introduced water-conservation provisions, and dual-flush is increasingly standard in new urban construction, but enforcement varies sharply by state. Many Indian homes still use traditional squat toilets, which actually use less water per use than most Western flush models.

Rainwater harvesting: 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. Bengaluru requires it on all new sites over 1,200 sq ft (around 111 m²) and on older sites over 2,400 sq ft (around 223 m²).

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Analysis grid

  1. Read each country's profile carefully. Then complete the analysis grid below.