Fallout3 for PS3, purified water?

There's a guy outside the gate to Megaton that wants purified water, Mitch? Mick? Anyway, I gave him a bottle and he said thank you, and now he just wants more! So is this like Fred in the Den in Fallout2, where if you paid off his gambling debt, he would later pay you back, plus give you a Power Fist and energy cells? Or is this thirsty guy just there to look pitiful so I'll give him all my purified water?