Thermal water In 1907, Fernand de Saintignon, an ironmaster, commissioned a 900-meter-deep borehole in Longwy in an attempt to discover a coal deposit usable for his blast furnaces. He found a tiny coal seam and, most importantly, at -353 meters, the Récollets spring, whose water is remarkably pure. He then turned Longwy into a thermal spa and built a hotel in 1912 to accommodate patients seeking treatment for arthritis.