'Solar Water Still' is a device to

Concept

A solar still works on the principle of solar distillation: sunlight heats impure or saline water inside a closed, transparent enclosure, the water evaporates leaving behind salts, microbes and other contaminants, and the pure vapour then condenses on the cooler sloping cover and is collected separately. The energy input is sunlight; the output is purified, drinkable water.

Application

Apply this principle to the named device. A 'Solar Water Still' is precisely a solar distillation unit: it harnesses solar energy to evaporate and then condense water so that the collected condensate is free of dissolved and biological impurities. Its purpose is therefore to make contaminated or salty water safe to drink.

So the function that matches the device is: produce potable (drinkable) water by using solar energy.

Why the other functions do not fit

• Pumping water moves water from one place to another and needs a solar-powered pump and motor; it does not purify water, so it is a different solar device, not a still.

• Generating electricity converts sunlight into electric power using photovoltaic cells; a still has no cells and produces no electricity.

• Merely producing heat describes a solar water heater or solar cooker; heat alone is only an intermediate step, the defining output of a still is the purified condensate, not warmth.

Result

A 'Solar Water Still' is a device to produce potable water by using solar energy.