President Xi Jinping has called for a “toilet revolution”, which will be the centrepiece of his “new countryside” drive. The goal is to improve the quality of life of the country’s 600 million villagers – the same number of people that India’s Narendra Modi is trying to wean from open defecation in India.

After riding to power in May 2014, the Indian prime minister launched the Swachh Bharat (Clean India) campaign with the aim of eradicating open defecation by 2019. The national campaign spans 4,042 cities and towns and includes the construction of 110 million toilets, the largest toilet building programme in the history of mankind.

So why are the leaders of the world’s two biggest countries making toilets a cornerstone of their legacies? The answer could lie in tiny Singapore.

As an independent nation state in 1965, Singapore was born into poverty. Lee Kuan Yew, the country’s first prime minister and founding father, who wanted to build a strong and prosperous nation, quickly understood the power of sanitation. Public health was poor and there were frequent outbreaks of cholera, typhoid and other waterborne diseases. Lee knew a sick nation couldn’t be productive but Singapore didn’t have the time or resources to build an expensive curative health care system. So he invested in toilet hygiene and clean water as a preventive health strategy, which was much cheaper and far more effective.

From Lee to Modi and Xi, the logic for investing in toilets is simple. One, toilets are the world’s cheapest medicine. Sanitation was voted the greatest medical milestone of the last 150 years in a poll by the British Medical Journal – higher than vaccines, antibiotics and anaesthesia, because passive protection against health hazards is often the best way to improve a population’s health.

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Two, toilets are GDP boosters. China and India, with their rich historic architectures, deep and diverse cultures and natural landscapes should be able to attract huge amounts of tourists as toilets become more widespread and accessible. Until now, dirty toilets or the absence of toilets altogether has been a tourism choke point.

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When Beijing was organising the 2008 Olympics, the China National Tourism Bureau was worried that if Beijing’s toilets failed, so would the Olympics. They renovated 4,000 public toilet blocks in 2004 and hosted the World Toilet Summit that year to showcase the new toilets at prime tourism spots like Tiananmen Square and the Great Wall at Badaling. Since 2015, the China National Tourism Administration has installed or upgraded 68,000 toilets. Another 64,000 toilets are planned from 2018 to 2020.

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Three, toilets mean dignity, and in some countries, safety. In India, 30 per cent of rapes occur when women go out to defecate in the open. Adolescent girls drop out of schools once they start to menstruate because there are no toilets to change sanitary pads. This affects their education and life outcomes, and perpetuates poverty. In China, students must clean dry toilets, putting them in contact with the faeces.

Beyond the government effort, India’s toilet drive is inspiring Bollywood movies such as Toilet: a Love Story. In January a new movie called Padman will feature menstrual hygiene. I hope toilets will find cultural expression in China too, which would greatly enhance the government’s efforts. This year is the 100th anniversary of Marcel Duchamp’s Fountain, the porcelain urinal voted the most influential artwork of the 20th century. There couldn’t be a better way, and time, to spread sanitation awareness by cultural means.

Toilets are a UN sustainable development goal. After years of successful advocacy by the World Toilet Organisation, the 193 countries of the UN General Assembly have now put sanitation on their national budgets and policy implementation agendas. If China and India, the two countries with the largest populations, can reach their toilet targets, we can achieve 60 per cent of the global sanitation goal. Hence Xi and Modi, with their focus on toilets, are actually effecting a revolution that is not confined to their countries but will affect the world in a much more profound manner.

Jack Sim is the founder of World Toilet Organisation and Schwab Fellow of the World Economic Forum. The World Toilet Organisation’s founding day, November 19, is now enshrined as UN World Toilet Day