For forty-four years, the future has been defined by a word: plastics. Our buildings are full of plastic materials, and tin box makes use of three in particular: polyethylene, polypropylene and polyvinyl chloride. Two of these materials have serious environmental benefits. One is a known killer. All three have their plusses and minuses.
We're using cross-linked polyethylene (PEX) tubing for the water supply pipes throughout the house. PEX replaces copper, which has a huge environmental footprint due to mining, smelting, processing, transporting and soldering. PEX is also cheaper (one-ninth the cost of copper pipe) and much faster to install.
Our rainwater cistern is made of polypropylene, which, unlike PEX, won't degrade in sunlight (a real plus for an object that will be constantly exposed to sunlight). Polypropylene (PP) tanks are less likely to promote microbial growth than metal tanks, and they have a smaller environmental footprint than metal. Like PEX, the polypropylene is recyclable at the end of the house's life cycle.
Since the PEX and PP will handle our drinking water, we checked to make sure that neither contains Bisphenol A, an endocrine disruptor that's used to make polycarbonate. Perkins + Will has developed an online "precautionary list" that they've initiated to keep track of products that are harmful to human health and the environment. The list is publicly available, which is a great example of generous, open-source knowledge-sharing in the profession.
The precautionary list has a long entry on polyvinyl chloride (PVC), the material we're using for our drain pipes. PVC production creates dioxin, which is a carcinogen that wreaks havoc on the people who work in PVC-producing plants. It isn't toxic once it's inside the house, unless it melts, but its production exerts a devastating toll on communities in Louisiana and the Veneto (see the excellent 2002 documentary, Blue Vinyl). This is one we wish we could avoid, and we're looking into alternatives, but we just haven't found anything cost-effective, yet.
The down side to all three plastics is that they are usually made from petroleum. This will change in the future as more plastics are produced from vegetable oils and other sustainable source materials, but, for now, sustainability remains a process of striking a balance between benefits and liabilities.