WHO officials say it is a hidden childhood killer, leading to more deaths among under-15s than tuberculosis or measles in 2012 and urge for more to be done "to tackle this preventable loss of life".
Director-general Dr Margaret Chan said: "Efforts to reduce child mortality have brought remarkable gains in recent decades but they have also revealed otherwise hidden childhood killers.
Drowning is one. This is a needless loss of life. Action must be taken by national and local governments to put in place the simple preventative measures articulated by the WHO."
Watch Michael Dunn from RLSS UK talks about the dangers, both obvious and hidden, of flooding and flood water at http://youtu.be/zjji-OFpBdk
The first WHO investigation of deaths by drowning revealed people under 25 contribute to more than half of all recorded deaths by drowning each year.
But experts warn rates in high income countries may be underestimated as official data fails to include every detail - including drowning from floods or suicides.
According to the report, drowning led to 140,219 deaths in under-15s in 2012, twice the number caused by tuberculosis (69,648).
The research suggests much more could be done to prevent drowning, including:
- Teaching school-age children basic swimming, water safety and safe rescue skills
- Training bystanders in rescue and resuscitation
- Setting boating, shipping and ferry regulations
To find out more water safety tips visit www.rlss.org.uk