Imagine taking a long, hot shower without wasting water and energy.

That’s the guilt-free promise of a recirculating shower, which continuously filters, sterilizes and reuses water that would otherwise go down the bathroom drain. The technology reduces water consumption up to 90% and energy use by 80% compared to a conventional shower, according to manufacturers of the devices.

“We are addressing two of the problems the world is facing, climate change and water shortages, without sacrificing the shower experience,” said Troels Grene, chief executive officer of Flow Loop, a Danish company that has developed a recirculating shower called the Eco Loop.

Flow Loop is one of several startups bringing the technology to market in northern Europe, with plans t…