The discovery of thousands of unregistered private swimming pools in France has brought the French tax authorities an unexpected windfall.

Over 20,000 underground pools were found after an artificial intelligence (AI) experiment.

They have generated about €10 million (£8.5 million) in revenue, according to French media.

Because they increase property value, pools can result in higher property taxes and are required to be declared under French law.

During a trial in October 2021, the software—which was created by Google and the French consulting firm Capgemini—found the pools on aerial photographs of nine French districts.

The trial included the regions of Alpes-Maritimes, Var, Bouches-du-Rhône, Ardèche, Rhône, Haute-Savoie, Vendée, Maine-et-Loire, and Morbihan; however, tax officials say it may now be implemented countrywide.

According to data portal Statista, there were more than 3.2 million private swimming pools in France in 2020, and business was flourishing even before the Covid epidemic.

However, as more workers choose to work from home, the number of pools installed increased.

A typical pool of 30 sq m (322 sq ft) is taxed at €200 (£170), according to the Le Parisien newspaper.

The software may potentially be used to identify gazebos, patios, and unreported home additions that affect property taxes, according to the tax authorities.

Le Parisien quoted Antoine Magnant, the deputy general director of public finances, as saying: “We are focusing in particular on home additions like verandas.

But we need to make sure the algorithms can identify large-footprint buildings and not just dog kennels or kiddie playhouses, he continued.

After Julien Bayou of the France’s Europe-Ecology Greens party did not rule out a ban on new private pools, there was a crackdown.

He claimed in an interview with BFMTV that France needed a “new relationship to water” and that the ban would only be used as a “last option.”

The difficulty, he continued, is to ensure that we have access to the essential water that we need.

He made these remarks while France battled its worst-ever drought, which has left over 100 municipalities without access to drinking water.

According to the national weather service Meteo-France, July was the driest month in France since March 1961 with just 9.7mm (0.38in) of rain.

Across order to conserve water, irrigation has been prohibited in parts of France’s northwest and southeast.