This transfer will lead to a substantial increase in water scarcity in terms of the amount of water available for irrigation compared to water demand for irrigation, as the projected decline in irrigation water use for China and some countries in the Middle East and North Africa shows. Water quality impairments can lead to increased competition among water users for the shrinking supplies of unpolluted water. Pollutants can include both human-induced pollution such as salinisation, microbiological contamination, eutrophication and excess nutrients, acidification, metal pollutants, toxic wastes, saltwater contamination, thermal pollution, and increases in total suspended solids, as well as natural pollutants such as arsenic and fluoride. Poor water quality increasingly constrains agricultural and economic development in densely populated regions that experience water scarcity and are plagued by poor wastewater treatment, particularly in densely populated Asia.