Across the world, 1 in 3 women risk shame, disease, harassment and even attack because they have nowhere safe to go to the toilet. That's 1.25 billion women - daughters, sisters, mothers, grandmothers.
Facing each day without access to this basic necessity is not just an inconvenience; it impacts on all aspects of life, and it is women and girls who suffer the most.
That is why, this World Toilet Day, we are joining international charity WaterAid in a calling for governments across the world to make good on their promises to provide the world's poorest people with safe toilets and clean water.
Poor sanitation and dirty water can have a detrimental effect on health. Every day, around 2,000 mothers go through the pain of losing a child to diarrhoea brought about through a lack of access to safe toilets and clean water. In fact, diarrhoea kills more children every year than AIDS, malaria and measles combined.
Having nowhere safe to go to the toilet also means an increased risk of shame, harassment and even violence for women and girls when they are forced to go out in search of a private place to go to the toilet.
A survey commissioned by WaterAid of women living across some of the slums of Lagos, Nigeria, highlighted this shocking problem. One in five women interviewed had first or second hand experience of verbal harassment and intimidation, or had been threatened or physically assaulted, in the past year alone when going to the toilet.
Lack of decent sanitation also affects women's productivity and livelihoods, impacting on their time and health. Finding a place to go to the toilet can take women away from productive activities for long periods of time. In fact, women and girls living in developing countries without toilet facilities spend 97 billion hours each year finding a place to go in the open. This is double the total number of hours worked every year by the entire labour force in the UK.
Women are often hesitant to talk about this issue, but with these experiences of fear, disease, indignity and violence being common wherever women lack access to safe sanitation, the world must take note.
Investing in sanitation and water works. For every £1 invested in water and sanitation, an average of £4 is returned in increased productivity. Since 1990, around 900 million women and girls have gained access to safe sanitation facilities, while over a billion have gained access to clean drinking water. This is great progress, but our efforts cannot stop here.
At the Sanitation and Water for All High Level Meeting in April, the UK Government committed to double the number of people they plan to reach with water, sanitation and hygiene by 2015.
We welcome this commitment and today ask the UK Government as well as other governments around the world to keep their promises to help achieve global access to sanitation and water.
Everyone can help support those women across the world living without safe toilets by signing WaterAid's pledge that everyone should have somewhere safe to go to the toilet at www.wateraid.org/1in3.
HuffPost Women sends stories about relationships, politics, sex, work, culture and body image, straight to your inbox three days a week. Learn more