Notice, that it's a playlist with a bunch of these case studies.
The device displayed in the video (the company makes a few different ones) didn't require watering at all, because it collects dew. It's also biodegradable, so there isn't a cleanup cost. They also provide physical protection for the sapplings, which can be important. It seems to add up to very high survival rate in tough environments.
Dew collection at night and massive evaporation of the Sahara during daytime. Not sure if this would be enough to sustain a medium sized tree. Whatever works in Netherlands may not work in Egypt.
The collected water does not evaporate. The linked case studies are in extreme climates, like a 1500-1900 meter altitude mountainside or a desert in Spain, not central Europe.
Rainwater refills it, evaporation blocked via siphon. Most deserts get at least 150-250 liters of water per square meter per year, often much more. [1] The boxes supply enough water for the roots to grow down to the capillary water below.
