Day Zero: green nudges to prevent a city’s water from running out

What unsustainable behavior needs to change:

Early in 2018, Cape Town (South Africa’s third-largest city) — nearly ran out of municipal water following a three-year drought!

It was the worst in recorded history, one, which even seasoned climatologists didn’t see coming. City managers prepared to implement emergency water rationing – the most extreme of which would have involved shutting off water to homes in the suburbs and to businesses outside of the city centre. Families would have had to collect a ration of 25L of water per person, per day, from 200 collection points around the city.

The Green Nudge:

To avoid having to implement ‘Day Zero’ extreme measures, the city used other methods to encourage reduced water use, including fines, increased tariffs, and Green nudges. 

Other cities facing similar human-induced climate change extremes can pull lessons from Cape Town’s experience. These can be universally applied, especially as extreme drought and urban growth continues to put pressure on dwindling water resources.

Green nudge 1 – Public recognition

When the city publicly praised “water wise,” residents by highlighting their names on the municipality’s website, people reduced their water usage. 

Green nudge 2 – Comparative water-use map

The Cape Town Water Map was an online tool designed to draw on social comparisons and public recognition, in order to encourage behaviour change. The digital map awarded households  with a green dot (per household and per month), to those that stayed within the city’s target water levels. 

Green nudge 3: Name-and-shame

The city released the names of the streets where the top 100 most wasteful household water users were, threatening to name and shame those who ignored restrictions. The mayor sent letters to individual households that were using more than 50kL of water per month; reprimanding them and asking them to lower their usage in order to behave in a more pro-social way. Households responded quite drastically by cutting their water use down.  

Green nudge 4: Raise the alarm, offer the solutions 

When the city released its water disaster management plan, it communicated firmly how urgent the situation was, but gave clear instructions on how people could reduce water use. Residents responded quickly and decisively, resulting in the single biggest reduction across the 2.5 year drought period. The take-home message: sharing clear, salient information with citizens during times of crisis is crucial in driving behavioural change, particularly if it also gives people a sense of what they can do to help fix the problem.