Water Quality by Country 2025

Water quality, particularly the quality of drinking water, is arguably the most essential requirement for the survival of not only mankind, but all terrestrial life on Earth. Despite its importance, water quality is not guaranteed and varies considerably throughout the world’s countries, influenced by natural and man-made factors.

Measuring the safety of the drinking water in each area of a country is vitally important, as it helps that country determine where to focus its efforts in order to ensure the long-term health of its citizens and the sustainability of its water supply.

How is the Safety of Drinking Water Determined?

Localized testing is the most common method of determining the safety of a region’s drinking water. In developed countries, testing may be conducted by the water utilities or by various local, state, or federal agencies. In developing and least-developed countries, testing may be much less consistent and reliable.

One of the most widely respected aggregators of water quality data is Yale University’s Environmental Performance Index, which tracks 40 performance indicators—including “Sanitation & Drinking Water”—in order to pinpoint the most environmentally friendly countries in the world. Additional performance indicators tracked by the EPI include environmental health, climate change mitigation, air quality, waste management, biodiversity, fishery populations, and more.

How is Water Quality Rated?

The EPI measures water quality in terms of “age-standardized disability-adjusted life-years lost per 100,000 persons (DALY rate) due to exposure to unsafe drinking water” (EPI). According to the DALY scale, a score of 100 indicates countries with the purest and least-contaminated water and a score of 0 indicates the 5% of countries with the most contaminated water on the planet.

Top 10 Countries with the Best Water Quality in the World (2022 DALY score)

10 Countries with the Worst Water Quality in the World (2022 DALY score)