The Water Merchants was the biggest caravan company in the Hub, controlling the water tower and, by extension, water distribution in the area. Their control over the oasis in was the root of the Great Merchant Wars and remained a point of controversy among the Hubbers for years to come as rival companies were forced to buy water to sell from the WM. As such, this company became very wealthy very fast, at the cost of developing some serious enemies, among them Decker of the Hub underground.
In fact, the head of the Water Merchants in 2161, Daren Hightower, was marked for termination by Decker, likely as part of his campaign to take over the water monopoly and rule the Hub abusing control of the water tower.
Compared to other companies, caravan guards get the worst paycheck (only 200 caps each way) although they are less likely to run into fierce opposition, and leave often, every five days. Additionally, a shipment of water can be bought to send it to Vault 13 and extend the time limit for finding the water chip by 100 days. In the unpatched version, this also lowered the Vault 13 invasion time limit by 100 days.