The vehicle, just purchased last spring, is currently undergoing major repairs in Saint Gallen.
The story of the severe damage emerged almost a week after the fire department took credit for dousing a hay field that threatened a residential area in the neighbouring municipality of Plan-les-Ouates.
The truck was parked in the field and later became engulfed in flames after fire fighters decided to tackle the blaze from two sides using a pincer movement, according to a report from Le Matin newspaper.
The immobilized new pump truck, which can handle 2,500 litres of water, was abandoned in the July 19th operation.
Using 10 other vehicles, fire department members brought the blaze under control after 15 minutes and after 160,000 square metres of of hay burned.
Fire department commander Nicolas Schumacher defended the tactics used, noting that decisions had to be made in a matter of seconds to avoid homes being damaged, Le Matin said.
Flames were several metres high when the first rescue vehicles arrived and the fire was within just 30 metres of housing, according to the report.
The cause of the fire was linked to fireworks.
The fire department said a 22-year-old man had fired a rocket into the field.
A financial estimate of the damage to the pump truck was not disclosed.