If your main worry about puddles is that you might absent-mindedly wander into one and get your feet wet, consider yourself lucky. Standing water can be a breeding ground for mosquitoes and other insects which can carry diseases such as zika, dengue or chikungunya, and therefore puddles represent a serious threat to human health in much of the world. Already vulnerable people are most at risk, particularly those living in favelas, informal settlements and refugee camps where drainage is poor or non-existent.