Solar Water Distilling

I saw videos about water distillation using only the sunlight and a few bottles on Youtube. In the videos, the distiller cleaned a lot of water in a short amount of time, but this seemed too good to be true, so I decided to test it. To make it, you would need two bottles: one full of "unsanitary" water, and one clean bottle attached to it by drilling a hole in each cap and connecting them with a tube. The bottles are slanted (the empty one higher), so when the "unsanitary" water evaporates, it would go through the hole and be collected in the empty bottle, making clean water. I left it outside for 24 hours, but I practically got no clean water from the contraption. Therefore, I believe this is not an efficient way to collect drinkable water in emergencies.