By C.F. ‘Chubb’ Michaud, MWS
In Parts 1 and 2 of this series, we looked at improving water productivity primarily through the use of reclaimed wastewater and treating it to substitute for new water as a potable source. Wastewater can be treated to various degrees depending on where it is heading next. Water recycling, which involves reusing the original water for some lesser-quality requirement, is a far easier process than is water reclamation. But first, let’s look at some important definitions so we’re on the same page.
Wastewater: used water that is no longer suitable for original use.
Recycled water: water which, as a result of treatment of wastewater, is suitable for a direct beneficial use or a controlled use (such as a substitute for potable water) that would not otherwise occur and is therefore considered a valuable resource. It is still wastewater and not considered potable. Again, it is only necessary to treat it to the quality needed to reuse it. With reclamation, the intent is to upgrade the used water all the way to its original use quality.
Reclaimed water: effluent derived in any part from sewage from a wastewater treatment system that has been adequately and reliably treated, so as a result of that treatment it is suitable for a beneficial use or a controlled use that would not otherwise occur and is no longer considered wastewater.
What are some of the definitions that describe the properties of wastewater and how can we use and reuse it?
Black water: water contaminated with food, animal or human waste (anything that will create a large biological oxygen demand). The ultimate recycle is returning it to the tap. After primary treatment and filtration plus disinfection, it can be re-used for non-potable irrigation, golf course watering, decorative fountains and industrial cooling (recycled water). Residential environments lack the sophistication to attempt to reclaim black water and should not even consider it. This should be the exclusive domain of continuously monitored and regulated municipal facilities.
Graywater: relatively clean wastewater such as from showers, bathroom sinks (not the toilet) and/or laundry. Notice that kitchen sinks are specifically excluded since the food waste and potential grease content makes then unsuitable for simple reuse. This water can be reused or recycled with very little treatment for landscape irrigation and other non-potable uses, such as flushing toilets where allowed by code. This water can quite possibly contain nutrients and even trace amounts of fecal bacteria. When captured, the initial catchment volume should be such that it is never stored for more than 24 hours. It should be filtered and disinfected and not stored for long periods. This kind of graywater is great for irrigation, but be aware that certain states, counties and local governments will sometimes prohibit the use of graywater on food crops. Industry experts currently recommend that graywater can be used on food and non-food crops (except root-crops, such as carrots and potatoes), but that the water itself should only be applied in a way that it will never be exposed on the surface or aerosolized, such as with a sprinkler. Typical usage is with a drip-emitter under mulch to not only protect from surface exposure but also to preserve precious moisture from evaporation. When planning on using graywater for irrigation, one should also be mindful to minimize the sodium content of the water to minimize the effect on the soil’s sodium adsorption ratio (SAR).
How can we improve our domestic water productivity? The primary rules of water sustainability are reduce, reuse and recycle.
Reduce your use. These basic rules of water conservation are listed in the order of preference and practicality. First and foremost, reduce water consumption. Every gallon not pulled from the tap improves overall water productivity for the home. Saving water by reducing usage doesn’t cost anything and saves more money than either reuse or recycle. It has the greatest reduction in carbon emissions as well, since pumping energy is also reduced.
According to my local city newspaper,1 simply by turning off the faucet while brushing teeth or shampooing hair can save as much as 500 gallons per month. Taking shorter (five-minute) showers saves up to 1,000 gallons per month. Doing only full loads of laundry and dishes can save an additional 200 gallons per month. Upgrading to water-saving devices, such as higher efficiency toilets and washers, can save an additional 600 gallons per month.
Read the water meter weekly to discover possible leaks in the system. It is estimated by US EPA2 that 10 percent of homes in the US have leaks of 90 gallons or more per day, wasting trillions of gallons per year per household. Leaks are often easily detectable and correctable and can save more than 10,000 gallons per year. If winter-time water usage exceeds 10,000 gallons per month, you probably have a serious leak. A leak of only one drop per second can waste as much as 3,000 gallons per year.
Major water losses can occur outside the home due to leaks in the irrigation system. A single 1/32 nd-inch crack in a pipe can waste more than 6,300 gallons of water per month,2 over half of total water use. Water plants early in the morning or evening to reduce evaporative losses to save 750 gallons per month. Water the lawn once a week to keep it viable but not necessarily green. This saves over 2,000 gallons per month. Water plants and shrubs with a bubbler or sub-surface/drip-irrigation emitters and avoid over-spraying, where water lands on impermeable surfaces like sidewalks and driveways. As much as 50 percent of the water we use outdoors is wasted due to inefficient watering methods and overspray.2 US EPA estimates that with common sense and economical water conservation devices and practices, the average home could reduce their consumption by 35 percent.3 Going all out indoors and out might reduce water use as much as 50 percent. That is a significant amount of water each year.
Reusing or recycling your water
How and where is our residential water used and what are the prime sources targeted for reuse? Water consumption varies widely from place to place within a region, state or even a community. Larger homes tend to have more landscaping and use more water outside for irrigation. City dwellers have less landscaping and use less water overall. For the purposes of illustration, however, we will talk in generalities and averages.
The average American home will use about 500 gallons of water per day (gpd).2 The overall average use across the country is 183 gpd per person. Approximately 50 percent is used outside the home and 50 percent inside. Of the 250 gpd used inside, 27 percent is used for flushing toilets (about 70 gpd or 25,000 gallons per year). If we focused solely on saving that amount, where would we find a suitable stream of collectible graywater? The shower and bathroom sink use about 33 percent of inside water and together could provide enough relatively clean water to at least flush toilets, which represents a net reduction of about 15 percent of annual household water consumption.
With the technological ability to recycle any water from any source for any application, the topic of water reuse could easily fill the pages of a very thick book. Residential reuse, however, is a different story. The fine art of the process, the implementation of monitoring and the reliability of the equipment is far too complex to even attempt at the domestic level without in-depth studies and planning. Even the simplest laundry-to-landscape schemes are actually far more involved than they might seem.
Managing expectations and setting realistic goals
When considering residential reuse, keep in mind 1) safety, 2) suitability of the source and 3) adequate treatment for the application. Landscape irrigation is sensitive to high sodium, boron and chlorine. Soft water, soap and/or bleach can sometimes rule out suitability requirements and the chemistry should be carefully evaluated. With over 50 percent of domestic water being used outside (landscape irrigation), it would be nearly impossible to capture enough used water from suitable sources, even if all of the water from inside the home was captured, including the black water from toilets and very dark graywater from the kitchen sink, garbage disposal and dishwasher. In the spirit of reuse, any water that can be recycled for any use that will replace using fresh, potable water is a workable plan. Even 50 gallons per day reduces household water needs by over 18,000 gallons per year. But at what savings and at what cost?
The best reasons to recycle domestic water
- You have exhausted all other available means of water conservation and sourcing and still need more water.
- You feel you have an overwhelming and true need to improve your water productivity.
- You are a conservationist with a large budget.
- You live on a desert island.
- It is the right thing to do.
One of the biggest problems with residential water reuse is collecting it. Even the simplest of recycling schemes will be complex and not cost-efficient. Saving 18-20,000 gallons of water a year will only reduce the water bill by about $100/year. If, however, you have no other choices and only if you have no other choices, it might certainly make sense to try, but conservation makes far more sense.
Using a combination of water-saving appliances, which include low-flush toilets, restricted shower heads, modern dishwashers and clothes washers, can save up to 36 percent. That’s more than one will ever save on water use through recycling. Drip irrigation and targeted bubblers will save thousands of gallons, when compared to spray-type sprinklers and flood irrigation. Drought-tolerant plants and xeriscaping will also save massive amounts of water. Remember: reducing use of fresh water has the same effect as recycling, only it is far less expensive and much less complicated.
To illustrate the needed equipment and safeguards to recycle graywater, I have developed the following schematic from my own Plan A graywater reuse system (see Figure 1).
I’m suggesting that reclaimed graywater only be used for flushing toilets and some landscaping and that only water from showers, bath tubs and bathroom sinks be collected. To collect the water, first flow it to a gravity sump. Do not disconnect the bathtub and sink from the drain. Use a feed connection with two valves (as shown) and make sure air gaps and check valves are in place so that bathroom drains can be diverted to the sewer, if needed. Adequate provision for drain overflow to municipal sewer or other code-approved discharge must be provided. A submersible pump will be needed to move water from the gravity sump through a strainer to the point of use or to treatment and storage. It is ideal to move the graywater to its intended use as quickly as possible to minimize chances of bacterial growth.
If the graywater is going to be stored for more than 24 hours, it should be properly disinfected with chlorine or another code-compliant technology. From there, use another submersible pump to pressurize the feed line to the points of use. The storage tank should also have provision for safe overflow to sewer to protect from pump failure or discharge pipe obstructions.
Many localities have approved graywater for irrigation under rules such as those mentioned earlier in the article. Very few have approved graywater for residential toilet flushing, since it requires more treatment stages, as show in the Figure 2.
As you can see, things are a lot more complicated than some well-intentioned people might make it seem. Human health can be seriously impacted when graywater systems are not properly designed or installed and they should not even be considered unless you follow the rules and adhere to industry best practices.
There is an easier way. It does not require tearing up your floors, walls and plumbing. It does not require permits. It is quick and easy and works for every bath/shower combination in your house regardless of location, even if there are isolated toilets. It’s called Plan B and it consists of a $1.98, two-gallon plastic bucket. That’s it!
Description of the process
Use the stopper in the bathtub or a small rubber sheet to plug the outlet of the shower. If the shower is shallow, store water in a larger five-gallon bucket for later use. When the need arises, scoop two gallons of water from the tub and dump it in the toilet. Voila! The city water hookup is still available and you don’t have to re-plumb anything.
In the course of discussions with industry expert Greg Reyneke,4 it became evident that reclaiming domestic water for reuse is not very practical and is extremely complex when compared to the potential benefits one would derive. There is never a financial case for residential graywater recovery; the return on investment is terrible. Rather, residential graywater recovery is used in extreme circumstances or where the homeowner wants to satisfy a greater environmental/emotional motivation. Therefore, it is best first to reduce the use. One can still use Plan B for further benefit and the pride of doing the right thing. Save the real recycling jobs for where they can be done safely and effectively.
- www.Fullertonwaterconservation.com. Article appearing week of Sept. 5, 2016.
- wwwEPA.gov/Water Sense US EPA website on Water Sense, June 2014 .
- www.easyearth.com website for good water conservation practices.
- Personal discussions with Greg Reyneke MWS August 2016.
Sodium adsorption ratio (SAR) is a measure of the suitability of water for use in agricultural irrigation, as determined by the concentrations of solids dissolved in the water. It is also a measure of the sodicity of soil, as determined from analysis of water extracted from the soil.
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