Challenges faced by Johor and Singapore in harvesting water from the Johor River portend what might lie ahead. Periodic dry spells have diminished the flow of water in the river. That impacts Johor's water treatment plants, as well as PUB's operations across the Causeway. Singapore is entitled to draw a specified amount of raw water from there under the 1962 Water Agreement, and is obliged to sell a portion of treated water to Johor.

The Republic extended more treated water to its close neighbour when the latter's water supply system was affected by river pollution last year. That caused the taps of 600,000 users in Johor to run dry. Pollution led to shutdowns again last month, this time impacting 1.8 million Johor residents. But Singaporeans weren't affected, although pollution did hit PUB's Johor River waterworks temporarily. Taps continued to flow here because PUB could step up production of desalinated water, NEWater and treated water from local reservoirs to meet demand.

Singapore's capacity to do this is under-appreciated. As supply pressures might grow - spurred by climate change, environmental degradation, weak conservation efforts or energy crises - can people afford to just carry on as usual? Such complacency could pose a danger as Singapore was ranked No. 1 among countries facing the greatest risk of high water stress in 2040.

Not knowing water rationing (even a limited simulation to heighten awareness of a precious resource), people's habits might not change. Demand for water might double by 2061, when the water agreement with Malaysia will cease. The extra amount for future needs "is water that we do not have now", as the PUB has warned. Banking on technology alone would be perilous. People must do their part too, by doggedly reducing household consumption, keeping waterways spotlessly clean, and reusing water safely.