Unlocking the Power of Grey Water

Posted by Rob Nicely on October 17, 2014
Unlocking the Power of Grey Water
Carmel Building and Design is working on a home that's following the strategies of the Living Building Challenge. They've recently posted the first video in a series that gives you a look at what they're up to (link to the left and below).

Along with this blog, Carmel Building & Design is introducing the first in a series of videos that showcase aspects of what they're doing in this Carmel Point home. 

In every house we build, we look for ways to increase energy efficiency and reduce related waste and costs. In the Carmel Point home we’re building, following the Living Building Challenge, some solutions we’re using include an awesome water-to-water heat pump, demand-controlled circulation system and what the industry calls “structured plumbing.” Together, these systems dramatically reduce both the energy used to heat the water and the amount of water wasted.

Let’s talk first about the water heating system that’s a lot more than a heat pump. It’s called the Nexus Heat Recovery System. Used in Australia, Nexus was introduced in the U.S. a couple of years back. It’s in a model home near Sacramento, but this is the first complete system installed in a residence in the U.S. We are excited about proving that such a “totally cool” system can work. Here are the highlights of this revolutionary system:

  • The system includes the NEXheater energy recycling water-to-water heat pump, the eWater Collector to collect grey water, NEXtreater grey water treatment system, and the NEXservoir treated water storage tank. The grey water treatment system is expected to complete the testing process in December and be certified as a NSF 350 “onsite treatment system for non-potable grey water.” This certification is recognized by the County of Monterey Environmental Health Department.
  • The house was plumbed for separate grey water and black water drain systems, both terminating in the mechanical room. Grey water from the laundry, bathtub, showers, and bathroom sinks will drain into the collection tank. The water heater will remove the heat from the grey water, then send the grey water to the treatment system. The treated water will be stored in a tank for exterior landscaping or non-potable use in toilets.
Here's how it works:
  1. When you take a shower or wash clothes, the warm water goes down the drain.
  2. The warm water is collected in the 75-gallon capacity grey water collector.
  3. Because hot water from the water heater tank was used, it starts the heat pump process between the collector and the heater, pulling the heat back out of the warm grey water.
  4. When that “batch” of warm grey water has brought the water heater temperature back up to 120°, the grey water is sent to the treatment unit.
  5. That batch of grey water is treated and sent to the treated water reservoir.
  6. The treated water may be used to flush toilets or irrigate landscaping.
  7. The system has the capacity to treat 200 gallons of grey water per day.
  8. When you stop using the system at night, the cycle is completed leaving the water heater hot, the collector empty and the treated water waiting in the tank.
  9. The cycle starts all over again the next time you use hot water.


Rob Nicely is the president of Carmel Building & Design. If you have questions, send an email to

This blog was reprinted with permission. You can view the original post here. 

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