What do a running faucet, a kitchen sink, and a load of laundry have in common? They all produce greywater, one of the most underutilized resources in your building.
Greywater recycling offers a way to repurpose discarded domestic water and go beyond low-flow fixtures and drought-tolerant landscaping. You’ve already paid for the water – why not use it again?
The Case for Greywater
Greywater reclamation is often pushed by building owners who adopt a long-term view of sustainability. A lower water bill is a worthy goal, but the bigger picture lies within your community.
Extracting water from local aquifers can have negative impacts on the ecosystem (Lake Mead, for example) and extreme weather conditions in recent years have generated a rash of droughts. Domestic water treatment is also an energy-intensive process that uses chemical disinfectants, among other measures, to clean water.
Any opportunity to adopt water conservation methods such as greywater recycling will benefit your building performance goals and the future stability of your region’s water supply.
Most facilities managers are familiar with stormwater, which is harvested after a rain. Greywater, however, is reclaimed from bathroom and kitchen sinks, laundry machines, and shower drains.
“Because greywater has soap, detergent, or biological material in it, you need chlorine or bromine to purify it,” says Bob Benazzi, a retired consultant for Jaros, Baum & Bolles (JB&B) Consulting Engineers. “Greywater should also be filtered before it’s released into your pipes.”
Note that water from toilets is off limits. Anything that comes into contact with human or animal waste is considered blackwater and requires the same purification precautions as a sewage treatment plant. Some facilities may classify shower and bathing water as a greywater option, whereas others feel the level of bacteria is too high, Benazzi explains.
Treated greywater is commonly recycled in restrooms to flush toilets and urinals and for drip irrigation – applications where it couldn’t be unintentionally breathed as an aerosol.
With added filtration measures, greywater can also be used for regular irrigation, sidewalk washing, and mechanical evaporation.
“The most challenging aspect of installing a greywater system is the initial cost of the piping,” says Jeffrey Kling, a mechanical engineer with Gibbens, Drake, & Scott. “Not only are you piping water from the collection sites to the storage tank, you’re also using a separate, pressurized pipe to move the treated water back to its end destination.”
These design requirements make greywater an attractive option for new construction, where the piping can be accounted for from the onset. Other system components include:
- Storage tanks are needed to collect several thousand gallons of water.
- Particle filtration will catch debris with coarse, fine, and micron filters.
- Sanitization options address bacteria or toxins with agents such as chlorine or bromine, UV light, ozone, or copper-silver ionization.
For existing buildings, have a consultant or engineer evaluate whether it’s feasible for your current layout to accommodate the necessary harvesting elements. A major bathroom renovation may also offer the right timing to add separate piping, Kling notes.
Like any other building equipment, greywater recycling needs ongoing maintenance and monitoring to remain effective.
“No mechanical system runs by itself. Greywater systems should be diligently maintained by experienced and well-trained staff,” Benazzi recommends.
Flush with Savings
A utility bill can show you how many gallons are consumed, but do you know where in your building they’re used? You cannot efficiently collect and redirect water if you don’t know which areas are the highest generators.
To gain a better understanding of your building’s water performance, conduct an audit or use sensors and metering to better understand your gallon consumption. Use this data to calculate payback and document performance after the system is in place.
Greywater is also a scalable solution and you may decide to recycle only a portion of your facility’s domestic water, Kling adds. It may be more economical to gather water from just one set of bathrooms or a single floor of the building than to capture all of the qualified drains.
From there, quantify the system’s benefits. This can be expressed as a reduction in overall water consumption or as the percentage of greywater captured and repurposed.
“Water is only going to become more scarce and the increased costs are going to impact every commercial building,” Kling stresses. “If owners are serious about occupying a building for 50 to 80 years, they’ll need to start using these water conservation techniques. Otherwise it will become too much of a burden to operate the building and it won’t be the investment it once was.”
Jennie Morton firstname.lastname@example.org is associate editor for BUILDINGS.