"I'm not jumping in after you." That was perhaps the last thing Sean Bickings heard before he sank under water in TempeA city in the south-western US state of Arizona. It is named after the Vale of Tempe in Greece., Arizona.

Bickings had begged police officers to rescue him. His partner pleaded with them too. Then, she had to watch as he sank beneath the surface, while the officers stood by.

Footage of the incident is shocking. But utilitarian philosopher Peter Singer believes we are no better than the officers.

He proposes the following. Imagine you are walking to a class when you see a child drowning in a pond. You could wade in and pull the child out, but your clothes will get muddy and you will miss your class. Do you save the child?

Every one of us would say yes. But, Singer continues, what if the child is many thousands of miles away. If you could save them, at little cost to yourself, should you still do so?

Yes, we would still say. Except, Singer points out, we constantly do not. Every time we buy new clothes or a nice meal, we are deciding not to send that money to help people in need.

Some cast doubt on Singer's reasoning. We tend to assume saving lives in the developing world is very cheap.

Yet the reality is not that simple. For example: one of the most effective ways of saving lives is to provide insecticide-treated mosquito netsA mesh curtain that is draped over a sleeping area to protect from mosquitos and other pest insects., which reduces cases of malariaA serious parasite infection transmitted by mosquito bites. It is one of the world's most lethal diseases..

The cost per life saved through mosquito nets has been estimated at around $2,300. Because, although the cost of purchasing and distributing each net is small, not every net saves a life.

So saving lives in the developing world is not as easy as pulling a drowning child out of a pond. A small donation will make a small difference, but Singer's emotive trade-off is based on false premises.

Others suggest this is the wrong way to think. They propose another thought experiment: if someone is abducting thousands of children and dropping them in ponds, should you spend your energy saving some of them? Or should you track down the person who is putting them in danger, and stop them?

They argue there is no point simply saving lives without doing anything to change the structures that put their lives in peril.

The £10 you donate might build a well in MalawiA country in southeastern Africa with a GDP per capita of just 5.29., but it will not change a banking system that has landed the country with unpayable debtsIn the 1980s, rich countries hiked up interest rates on the debts that poorer countries had taken out with them. The result is that many poorer countries are stuck making huge interest payments on debts whose principal they have long since paid off., preventing it from investing in its own water systems.

Yes: It is not morally inconsistent to save a person in front of you instead of someone thousands of miles away. It is only natural to feel greater empathy for an individual whose suffering you can actually see.

No: Whatever you might think, you have already answered this question in the negative. Every penny you spend on things for yourself could have gone towards improving the life of someone in need.

Or... It is not a question of saving someone who is drowning, but of draining the pond so no-one will drown there in future.

Tempe - A city in the south-western US state of Arizona. It is named after the Vale of Tempe in Greece.

Mosquito nets - A mesh curtain that is draped over a sleeping area to protect from mosquitos and other pest insects.

Malaria - A serious parasite infection transmitted by mosquito bites. It is one of the world's most lethal diseases.

Malawi - A country in southeastern Africa with a GDP per capita of just $625.29.

Unpayable debts - In the 1980s, rich countries hiked up interest rates on the debts that poorer countries had taken out with them. The result is that many poorer countries are stuck making huge interest payments on debts whose principal they have long since paid off.