old soil or bone-dry soil can become water-repellent (hydrophobic).
A surfactant or wetting agent can help. Store bought soils will come with this already added most of the time. Yucca extract is a common one for home use. You can even use dish soap if it's not odorized... you can google for a concoction using that.
if not too severe, just water slowly, let it soak in a bit and repeat until the job is done. I just did this about 1 hour ago while potting up, lol. My promix bale was sitting in the basement for 1.5 months and got fairly dry. i had to slowly get the top few inches moist, then after that could water as normal... even so, i came back 10minutes later after allowing it to settle/soak in and put a little more water down just to make sure there were no dry pockets.
Do you have a watering can or a tank with a wand -- the tank+wand come with nozzels that will help spread the water and allow it to soak in slowly. not necessary, but might be worth it. i take those nozzes off and water faster, lol. the wand alonw makes watering easier if you have to reach to a back row etc..
a properly constituted media doesn't have to worry about compaction. Solid medium becoms hydrophobic over time becuase of microbes and stuff dying and forming a microscopic "oily" layer around the particles. it's inevitable, but should not happen during the course of 1 grow.