Water quality: Clean at the source isn’t safe in the glass

The world has made remarkable progress in expanding access to drinking water over the past 20 years.

Yet 2.1 billion people, roughly one quarter of the world’s population, still lack safely managed drinking water.

Access to a water source does not necessarily mean that the water people drink is safe. 

Water can become contaminated during the process of collection, storage, or use.

As a result, even water that is safe at the source may not be safe by the time it reaches the glass.

The Atlas of Global Development 2026 explores this challenge and highlights how water quality remains one of the most difficult barriers to achieving universal access to safely managed drinking water.

Progress has been made—but the challenge remains

The chart above illustrates a shift in global drinking water access since 2000.

The proportion of people with access to safely managed drinking water has steadily increased around the world since 2000, while untreated surface water now makes up only a small share of the total (1.3 percent).

Most of the remaining 2.1 billion people have only “basic” water service, meaning they can reach an improved source within a 30-minute round trip, but the water is not necessarily on premises, consistently available, or free from contamination.

Addressing this issue is as much about proximity and reliability as it is about verified safety.

Safe drinking water means more than having a nearby water source

Safely managed drinking water requires more than an improved water source, such as piped water, tube wells, protected wells, or springs.

To be classified as safely managed, drinking water must be accessible on premises, available when needed, and free from E. coli contamination.

Across 94 countries with available data, water quality is the most common constraint on safely managed drinking water, and is the primary constraint in more than half of them.

Accessibility and availability are the primary constraints in roughly one quarter of countries each.

The challenges differ markedly across countries.

In Mongolia, limited access to water on premises is the primary barrier, while in Nepal water quality remains the key constraint despite relatively high levels of accessibility and availability.

Water quality remains the greatest challenge

Water that is safe at the source is not always safe by the time people drink it.

The Atlas shows that contamination can occur during collection, transport, storage, and household handling, such as an uncovered storage container, an unwashed cup, or a hand dipped into the container to scoop water. 

In many low- and middle-income countries, water quality is worse at the point of use than at the point of collection.

In 28 of the 30 countries with comparable data, the share of people exposed to contamination was higher when water was tested in the household than at the original water source.

These findings highlight why improving water quality remains one of the greatest challenges for achieving safely managed drinking water.

The world has made progress in expanding access to drinking water.

But achieving universal access to safely managed drinking water will depend not only on building infrastructure, but also on ensuring that water remains safe every step of the way – from the source to the glass.