About the numbers in this map

Access to water and sanitation in developing countries is not easy to measure. Official records of infrastructure investments can be incomplete, and breakdowns in services go unrecorded. The best way we’ve found to measure levels of access to water and sanitation is by actually asking people where they get their water from, and what type of toilet they use.

Household surveys and census data are regularly collected in developing countries. Household surveys take a representative sample of households and ask them a long list of questions (this is similar to how opinion polls work, and it usually produces reliable estimates). Census data attempts to survey every household in the country.

The World Health Organization (WHO) has produced some guidelines for surveys, to ensure that comparable questions are asked across the world. This enables us to make meaningful comparisons between countries and over time.

Most people don’t know the quality of the water they drink, as it is rarely subject to testing. The guidelines therefore suggest asking people what kind of source they take their water from. Some types of water source, and some types of toilet, are known to be safer than others, so this information is used to estimate the percentage of people with ‘safe’ access.

The term used for facilities that are likely to be safer is ‘improved’. For water, improved facilities include properly constructed wells with pumps, piped water supply and others; for sanitation, they include well constructed pit latrines, plumbed toilets and others.

Of course, sometimes improved facilities may have something wrong with them – they may be contaminated, or may only function some of the time – so it is important to remember that the real number of people who don’t have safe access is likely to be higher than these estimates.

When we look at the estimates, we can be sure that they tell us that at least this many people do not have safe water or sanitation, and possibly many more. This and other limits to the available data have led water and sanitation experts to propose comprehensive new monitoring methods to support a goal of access to truly universal and safe services.

There is a small team, made up of people from WHO and Unicef, tasked with monitoring the Millennium Development Goal (MDG) targets for water and sanitation. This team, called the Joint Monitoring Programme (JMP), collects all the surveys it can find for every country – currently, over 1,500 surveys. It looks at the estimates it has for each country and uses them to calculate the changes since 1990, publishing these estimates on their website.

In order to make our predictions, we have taken the annual change in the percentage of the population with access from the JMP estimates, and applied that to future years.

For the estimates of population we need to reach each year, we have used the United Nations Population Division medium estimate for the population in 2030, along with our prediction of access levels in 2030.

For the full data set please visit >

As we all remember from our maths classes, it’s important that we ‘show our working’. So, to see the detail of how the predictions were calculated, please see here >