Who are "Adireihem"?
Radak: They are adults (Malbim - rich people 1 ) who sent their youths outside the city, to see if they will find water. They came to the pits where normally is found gathered rainwater, or water is found there because it is very deep.
What are "Gevim"?
Rashi: They are pits in which water is gathered.
What is the meaning of "Shavu Cheleihem Reikam"?
Radak #1: They returned with their [empty] Kelim.
Radak #2: The Kelim returned empty [via one who returned them]. This is like "Efod Yarad b'Yado" (Shmuel I, 23:6), "l'Vilti Vo'u ha'Kelim" (below, 27:18).
Malbim: The youths died of thirst, and the Kelim returned empty.
Why are the Kelim empty?
Rashi: Rain did not fall.
Radak: There was no water in the pits - "Boshu Ki Vatach" (Iyov 6:20)
What is the meaning of "Chafu Rosheihem"?
Rashi: They covered their heads [Radak - due to shame that they did not find water].
Malbim: They covered their heads amidst mourning over their children.