The maximum penalties have been imposed after fatal truck crash in SA.

Valley Sweep Pty Ltd and Anton Zakic have pleaded guilty in the Latrobe Valley Magistrates' Court to a single charge each under the Occupational Health and Safety Act of failing to provide and maintain safe plant.

The company has now been fined $388,650 while Mr Zakic was fined $77,730 - the maximum penalties available.

The court was told Valley Sweep had entered into a hire agreement to provide another company with a water cart truck and a driver in April 2017.

Less than a month later, the 21-year-old driver was killed when the truck rolled while travelling down a long, steep, curved section of road near the town of Noojee.

A forensic engineer engaged by WorkSafe concluded the poor condition of the truck's brakes, including being improperly adjusted, was the primary cause of the crash.

It was revealed the truck had last undergone a major inspection and servicing by an external mechanic in December 2015.

Mr Zakic and another Valley Sweep employee had performed some maintenance and repair work for the company's fleet of trucks and had worked on the water tanker, but neither were qualified mechanics.

The court also heard the driver had not received any formal training in the operation of water cart trucks, which have unique handling characteristics, or any supervised training in driving a water cart truck in difficult conditions such as a steep or curved descent.

WorkSafe Executive Director of Health and Safety Julie Nielsen said there was no excuse for the employer's behaviour.

“This company's director made a reckless decision to perform service and maintenance work on the water truck himself, even though he knew he wasn't qualified to do so,” Ms Nielsen said.

“This failure to take reasonable care left a dangerous vehicle on the road and ultimately cost a young worker his life.”