Water story

Domestic water use is one of the focus areas in the Planet Clark Emerald House (PCEH). While domestic water supply is not an issue at present in Clark County, it could become a factor in the future, and it is always good practice to design looking forward. According to U.S. government estimates, at least 36 states are expected to face water shortages within the next five years. Demonstrating smart design now is planning for the future.

In estimating water use requirements, with respect to indoor and outdoor water use, consideration was given to both the supply side and ultimate disposal. The water story focuses on reducing internal/domestic use, which in turn diminishes supply issues, and helps minimize disposal treatment systems – whether on-site or at the municipal level. The landscape design uses mostly native plants with no turf grass and, therefore, presents nominal water needs.


The Planet Clark Emerald House (PCEH) project is helping to lead the way to affordable, high performance building by striving to meet the highest certification (Emerald) from the National Green Building Standard™ (ICC 700-2008). It is designed to use 70 percent less water in comparison to an average household of the same size. This effectively means 22 gallons per person per day versus the national average of 72.6 gallons per person per day (see graph below).

PCEH will also seek certification under the EPA WaterSense program, which only requires a 20 percent reduction.


In determining how to get to a 70% reduction, it was necessary to analyze a few data sources and make a few assumptions, as follows:

  1. EPA WaterSense program: The average US family of four uses 400 gallons of water every day.  On average, approximately 70 percent of that water is used indoors.   Therefore, 400 / 4 = 100 x 70% = 70 GPCD (gallons per  capita per day).
  2. Washington State Dept. of Ecology (WSDoE): WSDoE uses a study by the American Water Works Association to arrive at 72.6 GPCD (refer to graph).
  3. Ever Green Septic Design, consultant on the project, states that they are typically required to design for 240 gal/day/house (assuming 4 people: 240/4 = 60 GPCD).  This seems a bit lower than the national averages, but not too far off.
  4. Clark County Public Utility District (CPU) provided information that the average household uses 13,339 cubic feet of water annually.   At 7.48 gallons per cubic foot, that equates to 99,776 gallons.   According to the 2010 US Census, the average Clark County household is 2.65 people.  This works out to 103.15 GPCD.  If we apply the 70% indoor use factor from the EPA WaterSense program, then the average Clark County resident uses 72.21 GPCD for domestic needs, slightly higher than the national average.  Data from CPU on winter-only use – in effect dropping irrigation out – shows the average use is about 750 cubic feet / month / household, which factors down exactly to the national average of 70 GPCD.

So there were four targets to choose from in designing for the PCEH water use reduction target of 70 percent.

EPA WaterSense70 x .30 = 21 GPCD
WSDoE72.6 x .30 = 22 GPCD
EGSD60 x .30 = 18 GPCD
CPU70 x .30 = 21 GPCD


It will take some changes in habits as well as innovative products to get down to this level.


Because of the site’s wetland area, conditions will not allow for managing wastewater on-site (composting toilets, greywater systems, etc.).  The design concept anticipated water use analysis as of mid-January 2012  looks like this:

This seems like a reasonable lifestyle, but as with many building design targets, the awareness and training of the occupants can drastically affect the final consumption levels.


A sample selection of very water-efficient appliances will aid in meeting the 70% water reduction target:

Washing Machine
We’ve selected the Crosley CFW7700 $649 annual KWH=83 water gal =4,722

Energy Star Dishwasher



U-HEF toilet

A typical dual-flush toilet system averages out to about 1.2 GPF (gallons per flush) in actual use. We can do 30% better with a U-HET (Ultra High Efficiency Toilet).


Even with highly efficient low-flow fixtures and Energy Star appliances, it will be necessary for the family residing in the Planet Clark Emerald House to make wise choices every day with respect to their water use in order to meet the 70% reduction. 89 gallons per day for a family of four could be challenging at times depending on personal habits and health issues, but it is also an opportunity to show the community that it can be done and very comfortably.

A bio-feedback system could help the occupants maintain good water management.