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# Long description

Figure 8 The diagram in part (a) consists of a tall vertical cylinder, which narrows at the bottom. An arrow labelled 'contaminated water' points vertically down into the top of the cylinder, and an arrow labelled 'purified water' points vertically down from the bottom of the cylinder.

There are eight grey circles arranged in a regular pattern throughout the cylinder. A key identifies the circles as representing 'ion-exchange medium'. The area between the grey circles is coloured pale blue. Near the top of the cylinder there are a number of small yellow pentagons and blue triangles. The key identifies these as representing 'arsenic ions' and 'other contaminants'. There are also a few small green squares, which the key identifies as 'chloride ions'. Most of the yellow pentagons and blue triangles are attached to grey circles near the top of the cylinder. Near the bottom of the cylinder there are no yellow pentagons or blue triangles, but there are many more green squares. Most of the green squares are attached to the grey circles near the bottom of the cylinder.

Part (b) is a photograph which shows a man operating a hand pump attached to the bottom of two vertical cylinders, which are almost as tall as the man. The two vertical cylinders at the top are attached by pipes to the water supply. There is a bucket near the pump, and a child in the foreground of the photograph.