We need to change our minds about toilets. A woman from a small village in rural India, Anita Narre, shocked the nation when she left her husband two days after her wedding. But it wasn’t the speed of her decision that caused the astonishment; it was the reason. Outraged that her new home lacked a toilet, Narre refused to return until her husband built her one. Her story, which inspired my latest film, cuts to the very heart of one of the biggest crises facing my country today.

It wasn’t until I met Narre and other women like her that I understood the true scale of the issue. During my research for the film, I found out that half of India’s population – 564 million people – defecate in the open because they lack access to a toilet. But I didn’t know what this means for millions of women across the country. I had no idea about the fear these women experience every single time nature calls, or that so many women face assault and rape while going to the toilet outdoors.

The threat of violence and the leers of men mean that most women wait until nightfall before trudging out into the open. Many hold their bladders for up to 13 hours at a time, exposing them to urinary tract infections and other health problems.

This isn’t the only awful consequence of India’s lack of toilets. Defecating in the open spreads disease and pollutes drinking water, damaging the health of millions of my countrymen and women. Of the 1.7 million people worldwide who die every year because of poor sanitation and unsafe water, more than 600,000 die in India. Poor sanitation kills more Indian children under the age of five than anything else. Those who survive often grow up malnourished and stunted from diarrhoea, typhoid and worm infections.

That’s why I was so keen to attach my name to Toilet: Ek Prem Katha. The film tells the tale of a wife who refuses to return to her husband until he builds her a toilet. By bringing the issue of open defecation to Bollywood’s silver screen, I hope to inspire millions of people to tackle a problem that blights so many lives and deprives women and men of their safety, basic dignity and privacy.

The government already understands the scale of the issue. Our country is spending about $29bn (£24bn) on building millions of toilets, in a drive to get rid of open defecation by 2019. The problem is that many people still believe building toilets inside homes – where we wash, cook and worship – is dirty. Changing our minds will be essential if we are to stand a chance of tackling the sanitation crisis. Simply put, there is no point in building millions of toilets unless we use them.

This means the Indian government, NGOs and local leaders need to work with people to explain the dangers of open defecation and the benefits that toilets bring. But even that won’t be enough to change people’s minds. The toilets we build need to be connected to proper sewer lines, to avoid contaminating water sources. The waste needs to be properly treated or recycled. And our toilets must have sinks that work, so we can wash our hands and avoid spreading disease. We really need to show people that toilets are cleaner and healthier. Only then can we learn to love the toilet.

This isn’t just a problem that plagues my country. About one in three people worldwide lacks access to a toilet that provides safely managed sanitation. This puts all of us in danger. The lakes, rivers and groundwater that we depend on for our food and water are more polluted than ever. Most of the world’s wastewater is being dumped, untreated, into our rivers, spreading life-threatening diseases, killing fish and destroying ecosystems. As a result, an estimated 2 billion people are exposed to drinking water contaminated with faeces.

In December, world leaders will meet in Kenya at the UN environment assembly to find ways to combat water pollution. Water-borne diseases like diarrhoea are a major cause of death, especially in developing countries. The UN estimates that up to a third of rivers are contaminated with pathogens from poor sanitation, and that 3.4 million people, mostly children, die each year because of contaminated water.

In Kenya, countries will outline how they plan to tackle this deadly form of pollution. The cornerstone of life on our planet, water affects so much more than just our health. A lack of water increases poverty, inequality and hunger. It damages a child’s right to receive a decent education, often hitting society’s most vulnerable the hardest.

If we want to create a world that is healthier and fairer, it is essential that we work together to provide everyone with access to clean water and better sanitation. That is exactly what global leaders will do at the assembly when they commit to beating the pollution that plagues the water, soil and air that all of us share.

But it is not just governments that need to step up. The people I met as I worked on my latest film prove that individuals can effect immense change. Women like Anita Narre are transforming communities by demanding their right to live healthier, cleaner lives. These women are writing scripts for roles that all of us can play.

Each one of us has the power to change the minds of our friends, families and neighbours by educating them about the benefits of toilets and better sanitation. If we want the story to end happily – if we want a clean India where people live the healthy lives they deserve – then we must all learn to love the toilet.

• Akshay Kumar is an actor, producer and activist