Eutrophication (discussed below), acidification, toxic contamination and micro-pollutants all place pressures on human health, the cost of treating drinking water, irrigation and the maintenance of aquatic ecosystems. Water quality that is too poor for use exacerbates the problem of water scarcity. Pollution loads from diffuse agricultural and urban sources (fertilisers and pesticides, run-off from sealed surfaces and roads, and pharmaceuticals in animal and human waste) are continuing challenges in many countries.