Hycrete, which has devised materials and processes for waterproofing concrete, has landed NSF 61 certification, which means that contractors can build potable water tanks holding 200,000 gallons of water or more and add in the company's mixture. Why would you want to waterproof concrete? To prevent corrosion. The company's chemicals also allow contractors to forgo wrapping foundations and other structures with plastic membranes. Like many other building materials, concrete is undergoing a green retrofit. Calera, a Khosla Ventures company, is putting the finishing touches on a pilot plant (reported here first) in Moss Beach, California in which it will use plankton to capture carbon dioxide and produce minerals for concrete. Other interesting green building companies to look at: E2E Materials (biodegradable composite board), Arxx (insulated concrete forms), Icynene (spray foam insulation), Microposite (environmentally friendly building board), Integrity Block (earthen building blocks), Bottlestone (countertops from old bottle glass) Aspen Aerogels (deep-sea insulation in your home!), Cal-Star Cement (bricks), Icrete (custom and environmentally sound concrete) and of course Serious Materials. Construction consumes 12 percent of the energy in the U.S. and one heck of a lot of the waste product.