Answer: placing the water in several shallow pools in a sunny spot
Step-by-step explanation: Evaporation is a surface phenomenon which lets the higher energy molecules leave the surface of liquid in the form of vapors.
The molecules absorb energy from the surroundings and thus placing the water in sunny spot would let the molecules have more energy and they can easily escape into the atmosphere and thus contaminants will be left and water vapors can be condensed back to get it in liquid form.
Evaporation is directly proportional to the surface area of the liquid and thus several shallow pools will lead to more evaporation.