put some water into the bottom of the large glass bowl
place the small bowl carefully in the centre of the large bowl
cover the top of the large bowl with cling film so there are no gaps. Don’t pull it too tightly.
place a weight in the centre of the cling film so the film sags in the middle
place the bowl in direct sunlight and leave it for a few hours
The sun will heat the water in the bowl causing it to evaporate into water vapour. This will then rise, hit the cling film, cool and then condense forming water droplets. The droplets will continue to collect on the cling film until they become too heavy to stay there when they will drip down and fall into the small bowl in the centre . The weight is there to provide a sloping surface for the water to drip down and guide it into the smaller bowl.