“We wanted the water tower’s essence to remain intact,” said Mauro Brigham, of Bham Design Studio in Brussels, the architect responsible for the renovation and interior design.

Mr. Mets bought the building in 1996 for 30,000 euros (then about $43,000), after years of weekend trips on his motorcycle searching for the right tower. It had broken windows and crumbling masonry, but it matched his vision. And although it had been sold at a public auction, he tracked down the new owner and struck a deal.

“Some water towers are entirely empty,” Mr. Mets said. “But this one had six floors, which, along with its eight concrete columns, helped to support” the water reservoir at the top, which could hold 250,000 liters, he said, or about 66,100 gallons. “I began envisioning each floor as a separate living space,” he added.

As it turned out, buying the tower was the easy part. Because it was in an environmentally protected zone with restrictions on construction, Mr. Mets spent eight years trying to untangle red tape before he discovered a loophole that allowed him to pursue his dream. By registering the building as a site of historic importance (the tower qualifies as a World War II relic; it was completed by the Nazis in 1941, during the Belgium occupation), it could be converted into a private residence as long as the original structure remained intact.

Five years and 1.5 million euros (or $2.1 million) later, in 2009, the renovation was complete, and Mr. Mets jokingly christened his new home Chateau d’eau.