Calls have been made for people to respect the fountains in Queen Victoria Square after detergent was poured into the jets.
It meant the fountains had to be switched off, drained and refilled before being switched back on less than 24 hours later.
Councillor Daren Hale, portfolio holder for economic investment and regeneration, said: “Hull is a fantastic city with many picturesque areas such as the Rose Bowl, Hull Marina and Queen Victoria Square.
“The vast majority of people respect these areas, but unfortunately there are a handful that don’t. We’ve had instances of people putting washing-up liquids in the fountains in Queen Victoria Square and the Rose Bowl, which results in both inconvenience for residents and also a significant cost for the council.
“It’s fantastic to see so many people and families, especially in the summer, enjoying these recreational areas. This makes it even more upsetting, particularly for young children, when features like the fountains are forced temporarily out of use because of the actions of just a few. I urge all residents to take pride in their city, respect their surroundings and respect their fellow residents.”
The Queen Victoria Square water tank has a capacity of around 8,000 litres.
The fountain water is dosed with bromine as a disinfectant, so any of this chemical already dissolved in the tank water is lost when the system is emptied and therefore needs to be replaced.
The fountains are now operating as normal.