The spa world has a dirty little secret: even holistic healing can generate a big waste stream. (That organic-cotton robe you’re swaddled in?Laundered at least once a day.) However, key players are giving their own facilities a detox treatment. The newly formed Green Spa Network advocates earth-friendly measures that will minimize ecological impact, such as on-site organic gardening, reduced packaging, and chemical-free treatment products. The eight-member collective includes Napa’s Osmosis Day Spa Sanctuary (707/823-8231; osmosis.com), which has a worm-bin composting program that literally eats trash. Solage Calistoga (866/942-7442; solagecalistoga.com), owned by Auberge Resorts (also affiliated with the Network), taps natural geothermal springs for a hydrotherapy circuit of whirlpools and cold plunges. So what does the eco-friendly spa future look like?Expect the next generation to break ground farther off the grid, in places where renewable energy sources such as solar and wind power are abundant. And get ready to spa au naturel (already common in Japan). Real greenies don’t need robes.