We’re gonna need a smaller boat: Re-imagining residential water systems

Figure 1 – Where my fresh water comes from

In the US, we use more than double the amount of water per person than any other country in the world. An estimated 57% of our public water supply is used for residential use. The most recent 2010 USGS report estimates per capita US residential water use to be 88 gallons per day (gpd), which translates to an average household use of 300 gpd . . . and that’s just what’s going into the system.

An assessment of residential water systems should also consider system outputs. Wastewater infrastructure will need to grow exponentially in the coming decades to accommodate the projected 56 million new users connecting to centralized systems.

So, what does this mean for current and future policy on residential water systems?

In my opinion, we must downsize, moving away from costly large-scale water infrastructure maintenance and upgrades and moving towards small-scale and green infrastructure.

Why does water use matter?

Freshwater Supply Shortages

40 out of 50 state water managers expect water shortages under average conditions in some portion of their states over the next decade (as of 2014). In recent years, recurring droughts in California and other western states have drawn increasing attention to this issue.

Aging Public Infrastructure & Degraded Water Quality

The EPA estimated in 2013 that national public water infrastructure, most of which is 100+ years old, will need about $384.2B in capital improvements and upgrades to continue to provide safe drinking water in the next 20 years alone. Unfortunately, the $100M Flint water crisis might only be the first of many systemic water infrastructure failures, where the guarantee of clean public water on a municipal level will become increasingly costly.

How do our current residential water systems work?

Figure 2 – Residential water use breakdown [via EPA]


86% of US residents receive potable water from public supply while the remaining population draw groundwater from private wells. Once on the property, it is generally a 70/30 split between inside and outside water use, which can be broken down even further by appliance or faucet (as shown in the pie chart).


In the home, we create 2 types of wastewater: blackwater and greywater. Both can feed back into a municipal sewage collection system, a septic tank, or a lagoon system.

Blackwater: Includes wastewater containing bodily or other biological wastes from toilets, dishwashers, kitchen sinks.

Greywater: Includes wastewater from bathtubs, showers, bathroom sinks, and clothes washing machines

What are the alternatives?


To supplement the water they draw from the public water supply or private groundwater wells, homeowners can install rainwater harvesting systems on their roofs. Though it is not potable without proper filters, rainwater can be used for outdoor needs and toilet flushing.

Figure 3 – Rainwater Harvesting Example for Irrigation [via geograph]


Second, we could separate greywater from blackwater in our residential water systems, diverting greywater to a) the landscape b) irrigation c) toilet reuse. Looking at the pie chart again, we see that diverting greywater from a septic tank or municipal wastewater treatment facilities would shave off almost half of the amount of wastewater leaving a residence. Thus, with only an output of black wastewater, a homeowner could further reduce both the freshwater input and output from their system.

Figure 4 – Greywater System Treatment Example [via IDEP Foundation]

How can these alternative systems directly solve residential water issues?

Freshwater Supply Recharging

Rainwater harvesting would decrease homeowner freshwater needs, while installing greywater systems that discharge onto the landscape would contribute to widespread groundwater aquifer recharging, which has become a growing national issue. Both rainwater harvesting and greywater systems would increase both the resilience of homeowners and the public water supply in the case of extreme weather. 

Green Infrastructure & Improved Water Quality

With small-scale green infrastructure like rainwater harvesting, greywater systems, constructed wetlands, and waterless toilets, municipalities could scale down future large-scale water infrastructure investments. It would also save US households money on water and sewer bills. If the average US family spends about $500 per year on its water and sewer bill (not including taxpayer dollars going towards large-scale water infrastructure), estimated savings from a greywater system could be at least $150 per year. Depending on how much water you use and the sophistication of the greywater system, the payback period could range from 3-7 years.

Pertaining to water quality, greywater contains beneficial nutrients such as nitrogen and phosphorous from greywater-safe products that can enrich soil nutrients in irrigating gardens or fields which can reduce the need for fertilizer as well as add to nearby riparian and wetland habitat ecosystem health.

What is current policy?

Currently, there is no definitive federal regulation on greywater or rainwater harvest or other alternative water systems. Water supply and waste discharge regulation all occur at the state level.

Most states encourage rainwater harvesting to decrease a residence’s dependence on the public water supply especially in periods of drought. It has also become an important tool to reduce or prevent stormwater runoff into local water bodies.

Regarding greywater, however, few states have clear regulations or policies permitting small-scale or residential greywater discharge or reuse systems. Greywater systems, though understood by policy-makers to have water and energy conservation potential, would require radical changes to water infrastructure and administrative processes from reconfiguring residential plumbing codes to new on-site sewage discharge treatment regulations.

As a rule, most states are also hesitant to change over worries for public health, but this can be mitigated with technology standards much like the septic systems. And, if the septic industry makes $5B a year in the US, imagine what new niche industry and jobs greywater systems could create for certified plumbers, installers, and assessors.

What can you do as a residential water user right now to reduce water inputs and outputs?

  • Monitor and prevent water leaks. Smart home technology now allows you to install wireless water leak sensors in the house.
  • Switch to a low-flow or a waterless toilet of the incinerating or composting variety. Though a waterless toilet is not possible for or agreeable to everyone, low-flow toilets save on sewage bills. If you want to dig into the payback period, here is an example estimate of an 11.8 year payback period (assuming water prices do not change).
  • Replace old faucets with low-flow faucets in shower/sinks like Bricor that meet or exceed EPA’s WaterSense label standards.
  • Harvest rainwater in barrels for outdoor gardening/irrigation or install potable water filtration to allow a household to supplement or replace the public water supply (depending on annual average rainfall and state policy).
  • Communicate to policy-makers your support for re-assessing regulations and innovating processes for alternative residential water system technologies like greywater systems.

If state or federal adopted standards for greywater systems, small-scale technologies that are already available could replace large-scale public infrastructure. With smaller-scale water systems in place, we can prevent improper wastewater discharge, promote public and ecosystem health, and improve community-level resiliency to drought and flooding as a result of extreme weather events and climate change. It’s time we changed our water use strategy.

About Stephanie Erwin