Hydrophobic soil happens when the soil dries out beyond the normal dry stage of the usual wet/dry cycle. Once it is a hydrophobic state water will run through without being absorbed. If the person doing the watering does not know what is going on they are almost always going to fail to get the soil properly watered. The way to fix this is to give the soil a small amount of water and wait 20 to 30 minutes and then add some more water and wait. Eventually the organic particles in the soil has absorbed enough water that it is more damp than dry. At that point the soil can be returned back to the normal wet/dry cycle.
We see threads started or messages posted by growers who feel that their containers are light weight but when they try to water the soil the water almost immediately runs through and is in the saucer. They then want to know what is happening and what does it mean.
It can eventually become a problem if the grower does not realize what is going on. They can end up with a layer of moist soil at the top of the container from the watering sessions and another layer of moist soil at the bottom where the soil wicks up the run through water from the saucer. But, the center layer of soil in the container is dry and not doing anything for the plant.
Another way to find out it is happening is when a grower says that they pour water on the surface and it immediately comes out the bottom "just like it was running down the insides of the pot". And, that is what it is doing, following the hard side of the pot and just flowing through without properly soaking in.
The link below is from the Master Gardener web pages at the University of California and was one of the top links displayed when Mr Google responded when I typed in "hydrophobic soil".
https://mgsantaclara.ucanr.edu/garden-help/watering-hydrophobic-soil/