The Freshwater Species Population Index measures the average change over time in the populations of some 194 species of freshwater birds, mammals, reptiles, amphibians and fish around the world. Between 1970 and 1999, the Freshwater Species Population Index fell by nearly 50%, which constitutes a very rapid decline in population indices.

The leading causes of aquatic species decline and ecosystem degradation are physical alteration, habitat degradation and destruction, water withdrawal, overexploitation, pollution and the introduction of non-native species.

More than 2.6 billion people - 40% of the world's population - lack basic sanitation facilities.

Water is used in most means of generating power, and in many countries hydropower is the only really sustainable energy source.

During the 20th century, the world population almost increased fourfold, while water used in agriculture through irrigation increased sixfold and some major rivers approached an advanced level of water depletion.

Today, approximately 40% of the world's population, mostly those living in the world's poorest countries, is at risk of malaria.

Pregnant women and their unborn children are also particularly vulnerable to malaria, which is a major cause of perinatal mortality, low birth weight and maternal anaemia.

Drinkable water is becoming increasingly scarce. By the year 2025, it is predicted that water abstraction will increase by 50% in developing countries and 18% in developed countries, as population growth and development drive up water demand. Effects on the world's ecosystems have the potential to dramatically worsen the present situation, and current assessments suggest that existing practices are not adequate to avert this.

In a temperate climate, 33% of the total precipitation generally either returns by evaporation or evapotranspiration back into the atmosphere, 33% becomes surface water through runoff, and 33% recharges groundwater.

Water courses and lakes are affected by acid rain which falls directly into them and from water which runs into them. The problem is worst in the spring, when the snow melts. The pollution accumulated over the winter period is suddenly released as an 'acid surge' just at the time when many young fish and insects are most vulnerable.

At the species level, diversity appears to be high in relation to habitat extent; for example, globally the number of fish species per unit volume of water is more than 5,000 times greater in freshwaters than in the sea.

The world is facing a situation in which 2 billion people have no electricity at all, and 2.5 billion people in developing countries, mainly in rural areas, have little access to commercial energy services.

Malaria is caused by a parasite carried by certain types of mosquitoes. Humans are infected when bitten by the mosquitoes. Each year, there are 300 million to 500 million cases of malaria throughout the world and about 1 million children die of malaria. Reducing the mosquito population in households and communities by eliminating standing water can be an important factor in reducing malaria cases.

Coastal – and inland/freshwater – fishery harvests have continued to expand due to aquaculture, most of these ecosystems are stressed by overfishing, habitat loss and degradation, the introduction and presence of invasive species, pollution and the disruption of river flows by dams and other diversions.

More than half of the world’s population depends directly on mountain watersheds for water to grow food, to generate energy, to drink, and for other domestic purposes.