Why is the bald man digging in the desert at the start of Star Trek V: The Final Frontier?

Question

In the opening scene of Star Trek V: The Final Frontier, there is a bald man that is digging in the desert who is then approached by Sybok.

But what I don't understand is why he is digging in the first place. It looks like he's in an open stretch of desert, and I can't imagine what would be worth digging for out there. So why is he digging?

Answer 1

From the actual movie script, not a secondary source:

           FADE IN:

           1   EXT. DESERT - DAY                                              1

               Shimmering waves of heat. A flat unforgiving landscape 
               stretches to infinity. A storm of dust gathers on the 
               horizon, small at first, increasing in size as it 
               rolls toward us. Hoofbeats fill the soundtrack. Just 
               as the storm threatens to engulf us, A RIDER ON 
               HORSEBACK emerges.

               Superimpose: NIMBUS III
                            IN THE NEUTRAL ZONE
                            ("THE PLANET OF GALACTIC PEACE")

           2   CLOSER ANGLE - STRANGE HORSE AND RIDER                         2

               A twisted rhino horn juts from the snout of this odd 
               creature. The Rider spurs the beast, driving it onward. 
               His white robes flare out behind him like the wings 
               of an avenging angel. He rides like a man possessed.

                                                                        CUT TO:

           3   EXT. DRY LAKE BED - DAY                                        3

               Camera pans an arid expanse of scorched earth. J'ONN, 
               a ragged and malnourished homesteader of some alien 
               race, toils beneath a blazing sun, his back to camera. 
               He sinks an augering device into the ground, drilling 
               in vain for water. There are many hundreds
               of holes in the earth around him.

               J'onn reacts to the clop of approaching hooves. He 
               tenses, then whirls around clutching a crude home-made 
               pipe gun.

He sinks an augering device into the ground, drilling in vain for water.

This is the Revised Final Script dated November 21, 1988, with a foreword by Producer Harve Bennett. The original script can be purchased from the genuine Roddenberry family company.

This is backed up by another, highly trusted source, Chakoteya.net:

(out of a dust storm a horseman approaches an alien drilling for water. The horseman dismounts and addresses the alien)

Answer 2

TL;DR:

He is digging for the thing you need the most in a desert: water.

From the film's official novelization:

A STORM GATHERED on the desert horizon.

J'Onn paused in his work to stare beyond the wavering black bands of heat at the growing cloud of dust. Normally he would have headed back for the ramshackle shelter that served as home and waited the storm out there; today he did not care if the dust cloud swallowed him whole.

He looked back down at his work, at the small auger sunk into the scorched ground in a pathetic attempt to find water. This hole, like all the others, was barren; there was an utter lack of moisture in the soil. J'Onn no longer thought of it as such. To his mind, soil supported life, but this bleak, parched sand supported nothing—not his life, not Zaara's.

After Zaara's death the night before, he had wandered out to the field — once fertile, now no more than an extension of the desert—and begun to dig. Now the sun was overhead, and the field around him was dotted with hundreds of holes, many of them a few years old, made in happier times when water was not such a precious rarity. But most had been made during the gentle insanity that sustained J'Onn though the night and well into the day. - Star Trek V: The Final Frontier, novelization by J.M. Dillard.