The Water Cycle is a naturally occurring process that ensures a constant flow of water. Firstly, water is evaporated from the large bodies such as rivers and lakes. Together with this evaporated water, water released by plants and animals transpiring and respiring also travels up into the atmosphere as vapour.

     The large amounts of water vapour now coagulate together with dust particles and condense to form clouds. The nature and size of the clouds are influenced by several complex factors such as heat, climate, mountain ranges, the size and quantities of water bodies. When the resultant weight of the cloud overcomes the mutual forces of binding it falls to land as precipitation. The most common form is rain but others are snow, ice or sleet during wintertime especially.

   Normally is it this process of the water cycles that has been affected primely by human pollution. Waste gases such as Sulphur dioxide and carbon monoxide which are released by industrial factories and vehicles running on fuel condense in the water vapour and when the fall to the ground fall with an acidic pH. This is known as acid rain. The acid rain is corrosive in nature and may cause health problems to the exposed. This problem is currently very prevalent in many parts of the world due to unchecked industrialisation. Acid rain can cause damage to buildings and stone structures such as statues as well corroding them; exposure to people can cause them skin cancer too.

     The precipitate falls back onto land and erodes into the oceans and seas or directly back into oceans and seas. The oceans and seas then give rise to the continuous flow of water through the rivers and lakes and thus the amount of water on earth remains constant. The catchment areas for water built by man is known as a reservoir, the water here is treated and then pumped to water users all over the area.

The processes of treatment are mainly filtration and chlorination. In the event of acid rain, lime (calcium hydroxide is used to neutralise the acidic water).