They spoke after an engineer was reported saying the design by Gustafson Porter was a "disaster", which leaked hundreds of litres of water a day and caused subsidence. The only way to fix the problem, he said, was to smash down the fountain and start over.
But a representative for the Royal Parks said: "The fountain is not sinking, subsiding or leaking hundreds of litres. With any construction in open landscape there is a small amount of settling.
"This resulted in minor leakage in a small area of the fountain. As part of its annual maintenance, we replaced an area of grouting and improved the existing drainage. The fountain remains in good working order and attracts more than 800,000 visitors a year."
Director Mike Sugg of Cirencester Civil Engineering, which is working on the fountain in London's Hyde Park, said: "It is perfectly functional. You get occasional jointing issues caused by expansion and contraction and we have regrouted some parts."
He said the wet summer and large visitor numbers had prompted his team to lay extra drainage on a section of the porous path.
The engineer quoted in the press, Bob Monroe, worked for the firm for a few months before Christmas, he added.
Sugg said that Monroe was an ex-employee and his views did not represent the firm's.
Monroe could not be contacted and Mary Bowman, a director at Gustafson Porter, said the fountain was "quite clearly neither subsiding nor leaking".