Millions of children's lives are being put at risk each year because aid agencies and governments make wrong choices about health care priorities. This is the conclusion of a new report from the charity WaterAid.

It says that diarrhoea, caused by poor sanitation is killing many more children than HIV/Aids, tuberculosis and malaria combined.

The report says the global spending on HIV/Aids hugely outweighs the amounts spent on providing better sanitation.

This report highlights what it calls the inequity between the diseases that are killing children and the amounts of money being spent on them.

In 2004, it says, diarrhoea killed 1.8 million children around the world, but only $1.5bn (£1bn) was spent on sanitation in the two years between 2004 and 2006.

In the same period, $10.8bn (£7.1bn) was spent on HIV/Aids which was responsible for the deaths of just over 300,000 children.

The global response to diseases caused by sanitation is simply "not rational", according to the report.

The authors say that the lack of political will is to blame - sanitation is just not fashionable enough nor emotive enough to get politicians excited.

As a result, the disease burden is not informing aid decisions. And neither is the experience of history, according to Oliver Cumming, the author of the report.

"The only reason that we can see is this lack of political will, which is driving this neglect," Mr Cumming says.

"And it's all the more shocking when you consider the role that investments in sanitation played in the developed world.

"If you take the example of the UK, it was government-led investments in sanitation which, in fact, brought about the most significant reduction in child mortality at the end of the 19th Century - far greater than the advent of the national health system."

Mr Cumming says it is not a matter of choosing between one disease and another: developing countries could provide a balanced response to child mortality if previous aid commitments given by rich countries were actually met.