About UNEP UNEP Offices News Centre Publications Events Awards Milestones UNEP Store
GEO Year Book 2004/5  
UNEP Website GEO Home Page
Theme: FRESHWATER

Issues: Water quality
Theme: FRESHWATER
Indicators: Concentration of dissolved nitrogen in surface waters
Biological oxygen demand (BOD) in surface waters
Proportion of population with access to improved water supply*
Proportion of population with access to improved sanitation**
*MDG indicator no. 30 under Target 10, Goal 7
**MDG indicator no. 31 under Target 10, Goal 7

Water quality

Freshwater quality changes at the global, continental and drainage basin levels. In general, water pollution is growing, but there are also areas of improvement. Indicators for water quality include parameters for dissolved nitrogen and biological oxygen demand (BOD).

In water, nitrogen occurs as nitrates and nitrites. Sources of nitrogen in water bodies include fertilizer washed from agricultural land, acid rain and untreated or partially treated human and animal wastes. While surface water nitrogen levels in some parts of the world have gone down, in most regions they have remained stable or increased (Figure 13). Excessive nitrogen can harm human health and result in undesirable water quality conditions, including excessive algal and plant growth, and deoxygenation when plants and algae die and the oxygen is consumed as part of the decay process.

Figure 13: Mean concentration of dissolved nitrogen (nitrate + nitrite, mg/l N) in surface waters by selected region, 1979–90 and 1991–99

Note: data for Africa and West Asia not available
Source: GEO Data Portal, compiled from UNEP/GEMS-Water 2004

 

Concentrations of nitrates occur naturally in surface waters up to 5 mg/l NO3-N. Higher concentrations usually indicate pollution by human or animal waste, or fertilizer run-off. For drinking water, a maximum limit of 11.3 mg/l NO3-N is recommended. Higher concentrations can represent a significant human health risk (UNESCO/WHO/UNEP 1996).

Organic matter is decomposed by microorganisms in water and this process 'demands' oxygen. BOD is an indicator of the amount of organic matter present in freshwater. High BOD levels may indicate that water is contaminated with coliform bacteria and other pathogens and unfit for human consumption. Rivers in Europe and North America have shown a reduction in BOD levels over the past two decades (Figure 14). Unpolluted waters typically have a BOD of 2 mg/l O2 or less, while those receiving wastewaters or other organic residues can have up to 10 mg/l O2 or more (UNESCO/WHO/UNEP 1996).

Figure 14: Mean BOD (mg/l O2) in surface waters by selected region, 1979–90 and 1991–99

Note: data for West Asia not available
Source: GEO Data Portal, compiled from UNEP/GEMS-Water 2004

Water supply and sanitation

New data show that between 1990 and 2002, access to improved drinking water supply rose from 77 to 83 per cent of the world's population (Figure 15). Significant progress was made in Asia and the Pacific (+9 per cent). Progress in sub-Saharan Africa was also very impressive: from 49 to 58 per cent. In Latin America and the Caribbean, almost 90 per cent now have access to an improved supply (WHO/UNICEF 2004). However more than one billion people continue to use water from unimproved sources, nearly two thirds of whom live in Asia.

Figure 15: Population with access to improved water supply (% of total) by region and global, 1990 and 2002

Note: data for Europe not available
Source: GEO Data Portal, compiled from WHO/UNICEF 2004

Global sanitation coverage rose from 49 per cent in 1990 to 58 per cent in 2002 (Figure 16). About 2.6 billion people - half of the developing world - still live without improved sanitation. Though major progress was made in the Asia and the Pacific region, less than half of its population currently have access to improved sanitation. In Africa, coverage has increased by 4 per cent to 43 per cent over the same period of time.

Figure 16: Population with access to improved sanitation (% of total) by region and global, 1990 and 2002

Note: data for Europe not available
Source: GEO Data Portal, compiled from WHO/UNICEF 2004


Earthprint.com Order the Book