Once the bathwater is drained, the toilet flushed or the laundry done, few give a passing thought to the wastewater that leaves our homes. But chemical engineer Will Tarpeh might change your mind, if you give him the chance.

Tarpeh says that that water is a literal mine of valuable chemicals. Chemicals like nitrogen, phosphorus and potassium make great fertilizers. Lithium can be used in lithium ion batteries. And even pharmaceuticals could be recovered and reused. In fact, Tarpeh points out that if we could harvest all the world’s urine, it could supplant 20–30% of our nitrogen needs — and in some places can be cheaper to do than existing production and transport methods.

Waste, Tarpeh says, is just a state of mind. His “pipe dream,” he says, is to develop next-generation treatment plants on the neighborhood or even household scale able to extract the valuable chemicals in water most would rather send down the drain. Tarpeh tells bioengineer Russ Altman all about it in this the latest episode of Stanford Engineering’s The Future of Everything podcast. Listen and subscribe here.

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