The firm has fitted the Siemens Datatrak Automatic Vehicle Location System to 200 vehicles and uses it to monitor location to help in pinpointing which staff to send to see customers.
The utility carried out a six month trial before committing to the system a year ago and undertook a high-profile campaign to deal with any staff concerns over the use of the system.
Dave Watkins, head of regional operations at Wessex Water, said: 'We identified efficient fleet management as the key to improving operations in a number of business disciplines and increasing levels of customer satisfaction.
'The effective deployment of both human and physical resources would not only increase efficiency throughout the business, but also result in customer responses being dealt with more effectively, and faster.
But he admitted that staff were apprehensive about the benefits of using the system, until they were persuaded that the company was tracking the vehicle, not the individual.
Watkins added: 'The aim is to drive down the mileage through effective route planning and job allocation, thus having the vehicles on the road for shorter periods of time.' Staff concern over the use of so-called 'black boxes' has been a stumbling block for many companies looking to introduce the systems.