You don't need the full force of the water for every second that you're in the shower, but constantly turning it up and down at the taps can be tricky. That's where the Reva shower head comes in, as it automatically reduces the flow whenever you step back.
Manufactured by San Francisco-based startup Oasense, the Reva was invented by co-founder Evan Schneider when he was trying to find ways of saving water during the California drought. He realized that when people are in the shower, they require little if any water flow when doing things like shampooing or lathering soap.
The resulting head can be installed on any standard shower arm. Its electronics are powered by a built-in hydro-turbine generator, which is spun by the flowing water and connected to an integrated battery.
When the user wants to start showering, they just turn the taps to the desired temperature. The Reva responds by initially running the water at its 100% flow rate, which is 1.8 gallons (6.8 l) per minute. Once the device's temperature sensor detects that all the residual cold water has been purged from the pipes, and the incoming "new" water is at the selected temperature, it reduces the flow to about 0.3 gallons (1.1 l) per minute – or approximately 15% of the maximum flow.
When the user steps in, an array of infrared sensors in the Reva detect their presence beneath the shower head, and bring the pressure back up to 100%. Whenever they step back to shampoo or whatnot, though, the flow is temporarily brought back down to 15%. And no, the device doesn't incorporate any cameras, nor does it transmit any data to the internet.
Additionally, by pressing a button on top of the Reva, the user can keep it at 100% full-time (for one showering session) if desired. It will default back its flow-adjusting mode on its next use.
According to Oasense, users have reported water savings of over 50% – of course, your mileage may vary. Should you be interested in getting one, the Reva shower head will set you back US$350.
Source: Oasense via IEEE Spectrum