Four thousand children are dying every day from diseases caused by unsafe water and poor sanitation.

Diarrhoea is the second biggest killer of children under five in the developing world and kills more children than Aids, TB and malaria combined. Without improved sanitation children will not get to school. This is a daily disaster that can be solved. Solved through investment and good governance – through the UN, governments, the private sector and NGOs like WaterAid working together. We have seen the dramatic change to people's lives that safe water makes.

Yet despite this, only 32 per cent of the aid allocated for water and sanitation goes to the low income countries where the need is greatest. Investment in sanitation and water will also enable the other Millenium Development Goals (MDGs) to be met. Girls will stay at school after puberty if there are decent toilets and women and girls will be healthy, freed from the burden of water carrying, indignity and disease.

This is a critical year for international leaders, halfway through the International Decade for Water, two years after the International Year of Sanitation and approaching the 10-year milestone towards the MDG targets. Targets have been set and commitments made. Drinking water supplies and sanitation are critical to ensuring all the MDGs are met. At the current rate the MDG for sanitation will not be met in sub-Saharan Africa until 2206, almost 200 years too late. We look to governments and the UN to galvanise world leadership and bring to an end this crisis. The high-level ministerial meeting at the World Bank in April will focus on sanitation and water for all. This will bring together the UN, ministers from North and South to take concerted action and to demonstrate their commitment.

We must better target investment to low income countries and those living in poverty, co-ordinate efforts and take accountability for the water and sanitation crisis. Investment in sanitation brings economic and social return ($1 invested brings a $9 return according to WHO). Failure to invest will lead to the failure of other MDGs.

This is an edited extract from a speech given by the chief executive of WaterAid to a UN General Assembly Debate on Monday