Water is used to put out most fires.
Foam is used to put out fires involving flammable liquids like petrol and oil. In London there is usually a plentiful supply of water from hydrants. Sometimes we use water taken from rivers or ponds. If the water is running out we can use special hose laying lorries to allow us to pump water over a long distance. This means that we can pump water from where we can find a supply to where we need it.