Hi-tech loos that use little or no water and can recycle waste products safely and sustainably promise to give billions of people around the world access to much-needed sanitation. So why do so many still lack this basic amenity?

About 2.3 billion people still lack basic toilets, according to the World Health Organization (WHO). And 4.5 billion don't have safely managed sanitation, with waste disposed in a way that won't contaminate drinking water.

Each year contaminated water kills half a million children under five through diarrhoeal diseases, the WHO says.

So many inventors, entrepreneurs and research institutions around the world have been working on hi-tech loos that can function without the need for expensive mains sewerage systems.

To read more from the BBC website on this article, click here.