Composition of Matter

Pure Substance

Type of matter with a fixed composition that cannot be separated by physical means.

• Element- substance made up of atoms with same identity. E.g. gold, helium, aluminium.

• Compound- atoms of two or more elements combined. E.g. water (H20), carbon dioxide (CO2)

Mixture

Material made up of two or more substances that can be separated by physical means.

• Homogeneous- mixture in which different materials can be easily distinguished. E.g. pizza, fruit salad, granite.

• Heterogeneous- mixture in which two or more substances are uniformly spread out. E.g. vinegar, salt water.

Water: The universal solvent

Water Uses

The main uses of water are for agriculture, industry and household use. Industrial use of water increases with country income, going from 10% for low- and middle-income countries to 59% for high-income countries. Source: WBCSD (2009)

Agriculture: In many developing nations, irrigation accounts for over 90% of water withdrawn from available sources for use. In England where rain is abundant year round, water used for agriculture accounts for less than 1% of human usage. Yet even on the same continent, water used for irrigation in Spain, Portugal and Greece exceeds 70% of total usage.

Industrial use: After agriculture, industry is the second largest user of water – be it for the production of electricity, as process water, for mining, as a means to dispose or discharge waste etc. The amount varies heavily depending on the type of industries, and so does the pollution resulting from its use.

Domestic use: By now, the water we use directly in our homes accounts for the smallest part of water use – yet it is essential for our survival: for drinking, preparing foods, and for washing ourselves. The consumption varies greatly – for example, from as little as 10 L per person an day in low-income areas in Ulan Bator (Mongolia) (World Bank 2010) to almost 600 L per person and day in the United States (WBCSD 2009). A minimum of 50 L per day as a basic water need is recommended (FALKENMARK 2005; WATER ENCYCLOPAEDIA 2010).

Water scarcity is a complex problem - it is one of unsustainable use, mismanagement and a lacking and holistic water governance. As so often, it is the life of the poor who are affected most: by water related disease, by degraded and dangerous environments, by a lack of food and water for hygiene. Almost one billion people do not have access to improved water sources, and 2.6 billion do not use improved sanitation options.