Water Traders of the Endless Sands

In the The Endless Sands, water is rare. The vast majority of the massive desert is far from any source of water, and is almost completely devoid of life. What little fresh water that can be found there is in a small number of oases scattered throughout the eastern reaches of the desert, and along with it nearly all life. The lack of water in the rest of the desert makes surviving there almost impossible.
However, a valuable resource is found within the desert. Known as sun gems, or sometimes as the Light of Athis after the sun god, these yellow crystals emmit an amount of light similar to a torch. As, unlike other light sources, they emit this light indefinitely with no fuel, they are extreamely valuable, but also extremely rare. Thus, most of the crystals found near the oases were harvested long ago.
To find sun gems now, the crystal miners must travel far deeper into the desert. Expeditions traveling into the desert must take large quantities of water with them, which they usually must purchase from the oasis cities. These cities, often with walls built to encompass the entire oasis to deter thieves, tend to sell this water at obscene prices, knowing the miners will pay a great amount so that they can access the crystals. The prices often cause unsuccessful expeditions to leave the desert greatly in debt, and more then a few destitute travelers have been turned away from the cities, left to die in the desert.
Sun gems tend to grow more commonly in frequently in certain areas, and often expeditions that happen upon them will stay in the area for extended periods of time, as long as a few weeks in some cases. This requires extra water to be shipped to them, and the expeditions will often hire water traders from nearby cities to supply them. These water traders bring the water in large barrels, carried on the backs of giant sand lizards native to parts of the desert, and often travel with as many as a dozen armed guards per barrel to protect their cargo. They tend to charge far more then even the oasis cities, often taking payment in the sun gems themselves.
In most cities, the water traders are controlled by powerful cartels, who use violence and intimidation to give themselves monopolies on water shipment. Those who attempt to bypass their control often appear to go missing in the desert, before their bodies turn up mysteriously near the city gates, showing clear signs of a violent death. The leaders of these cartels often grow extremely wealthy, and often dwell in palaces within the oasis cities that rival even the cities rulers in size and granduer.
A smaller crystal trade also exists in the west of the Endless Sands, along the coast of the Howling Sea. Here the water can be shipped by boat, but mining expeditions are largely restricted to areas near the coast, leaving vast stretches of the desert inaccesible. Much of the deserts interior is completely uncharted, and appears to be uninhabited by both humanoids and any other known forms of life.