This is the first of three articles about water, its sources, treatment, use, and potential reuse when living off the grid.
By L. Fred Roensch, PhD
Part II. What is “grey”, “black”, and “white” water Can they be recycled?
Domestic water is usually discussed in terms of three types of water: “white water” or potable drinking water, “grey water” or water that has been used in the home for showers, cleaning, laundry, kitchen, etc but excludes toilet flushing water, and lastly “black” or toilet wastewater. Each type of domestic water will be discussed separately.
“Black” water or toilet wastewater
It is important to note that nearly 40% of the water used in a home (see pie chart) is in the bathroom, primarily for flushing the toilets. Therefore, if water conservation is a major concern or desire, serious consideration should be given to installing compost toilets rather than flush toilets.
If a waterless or a virtually waterless compost toilet is used than no “black” water will be produced. However, if a compost toilet is operated or designed improperly unacceptable odor can occur. Usually a fan is used to eliminate odors. There are a large number of treatments available to reduce or eliminate or reduce odor: perfumes, masking agents, adsorbents, oxidants, bacteria etc. One “natural” adsorbent is a humic/bacteria material called histosol (www.organicproducts.com). It is used widely in “porta-potties” to virtually eliminate odor and at the same time add organic biodegradable carbon to the compost.
The compost is removed periodically and applied to flower gardens or added to potting soil. However, many homeowners continue to prefer water-flushing toilets.
The water used for flushing the toilets does not, in most states and jurisdictions, need to meet potable water specifications. That’s the good news. However, regardless, the resulting wastewater must be carefully handled because of the potential for contamination with water borne pathogens, i.e., disease causing bacteria. Wastewater from the toilets must be maintained separately from the domestic potable drinking water.
Wastewater from the flush toilets is most frequently sent to a septic tank or other waste water system. A septic tank system requires the soil pass a “perk” test. A percolation or “perk” test determines if the soil used by the septic tank effluent distribution system will permit the water to easily enter the ground. Incidentally, some localities permit use of an above ground septic system but the ground must still pass the “perk” test. The perk test is the second highly recommended test if a septic tank will be installed, beside the well water quality tests (See Part I), that should be done before deciding to buy land for an off grid home.
An alternative is a wastewater garden. This is a relatively new innovation that can use both the “black” wastewater and the “grey water” (see definition below) in a garden1.
Another alternative to sending the wastewater from the toilets to a waste treatment system is to use anaerobic (no oxygen) bacterial digestion of the waste. Anaerobic digestion of the wastewater from the toilets will produce methane gas-a fuel. This gas can be compressed and used for heating, fuel for vehicles, and fuel for an emergency generator, or even a hot tub, grill or swimming pool. That’s the good news. However, it is unlikely that a single home would produce enough waste to justify the cost of the equipment required to digest the waste, compress the methane. Also, untreated methane gas from anaerobic digestion contains hydrogen sulfide that must be eliminated to prevent sulfur dioxide air contamination and corrosion in the equipment. Lastly, it is important to realize the BTU content of anaerobic digestion methane is lower. As a result the burners in a furnace, or other device must be modified to use methane rather than “natural” or propane gas.
Nevertheless, a group of homes could justify an anaerobic digester and the other equipment required for production and use of the methane. Of course, this would require collection of the wastewater from the toilets and construction and operation of an anaerobic digester facility.
Regardless, of the wastewater system selected, be sure to check with the local health authorities for assistance and regulations that may apply in your area.
Grey water2 is wastewater from the showers, tubs, kitchen sink, dishwashing, and laundry, etc, excluding the wastewater from the toilets. This water contains some bacteria and suspended solids but can be used, usually, safely, to water plants, the garden, greenhouse, and yard. However, if baby diapers are washed in the laundry or someone has an infection in the home the grey water would be contaminated and should only be sent to a waste treatment system such as a septic tank. Care should be taken to minimize the suspended solids and toxicity of the grey water and avoid using or adding toxic substances into any part of the grey water collection system. It is generally recommended that grey water not be stored over 24 hrs because of the potential for bacterial growth in the water. Because of this potential, in some locations, retention of grey water is prohibited or restricted to a maximum period. In that case, a sump pump with a timer can be used to remove the grey water if not used.
“White” water or potable drinking water
A little history is appropriate when discussing potable drinking water. It is widely believed that the single biggest increase in human life expectancy is advances in modern medical care. Actually, most professional health officials disagree. They strongly believe the single action that increased human life expectancy and child survival rate the most and reduced the potential for epidemics of water borne disease was implementation of consistent treatment of drinking water. In addition, this was coupled with installation of separate sewer wastewater treatment system.
Many individuals are very concerned about municipal treated municipal drinking tap water. Most health professionals believe potable water that meets the EPA standards is “safe” to drink. Nevertheless, fear sells.
To meet the potable drinking water standards set by the EPA3, all lines, filters, filter media, fittings, pumps, lines, chemicals, etc. i.e. in fact, anything that contacts potable or potentially potable water must be certified by the National Sanitation Foundation (NSF)4. NSF is an independent privately run organization that is authorized by the US EPA but is funded primarily by fees from the suppliers of the equipment and chemicals used in treating and distributing potable water.
Another organization that is involved in drinking water is the American Water Works Association 5.
Worldwide, clarification or filtration followed by chlorination5, is the most widely used treatment for potable drinking water. It is the least expensive and the easiest to monitor. The filter or clarifier is usually treated with chlorine or other oxidant because they are a potential source of bacterial contamination of the drinking water.
Because of the World War I history of using chlorine in combat, ozone is used widely in Europe. A few locations use ozone as a primary disinfectant in the U.S. However, most follow the ozone treatment with chlorine because of chlorine’s persistence in the water and ease of testing for a residual at end of the system.
I am very familiar with one specific example of bacterial contamination from a filter, which resulted in severe illness. In this specific case an older couple lived on mid-western farm where no municipal water was available. The water was pumped from a pond, filtered through a very large sand filter, and then stored in a cistern. A separate water system collected water from the roof of the home. This water was filtered through sand/(GAC) filters and also stored with the filtered water from the pond in the cistern. To further remove the last traces of suspended solids the water was filtered using a spiral wound cartridge filter. The water was continuously chlorinated to maintain a free chlorine residual at the end of the distribution system. Everything was fine for a couple of years. Suddenly they had great difficulty consistently maintaining a free chlorine residual and both individuals periodically developed severe diarrhea. It was approaching a life-threatening situation.
After testing the water at several points it was discovered that the cartridge filter was a major source of bacteria. Apparently the final filter had become a constant source of bacteria that periodically overwhelmed the chlorination treatment system. The system was sterilized using hyper chlorination. This treatment stopped the loss of free chlorine residual. With changing the filter frequently, the problem was stopped. I am especially happy because this couple was my parents!
One domestic off-grid water system is shown in the drawing below. Obviously, this system would be modified drastically depending on the source or sources of water available. However, the minimum source of water would be a stream or a well plus, hopefully, significant water collected from the roof of the home.
Acknowledgement: The pie-chart showing domestic water use is used with permission from The Renewable Energy Handbook- A Guide to Rural Energy Independence, Off-Grid and Sustainable Living by William H. Kemp”, Aztext Press www.aztext.com
- Consult Appendix 12 in “The Renewable Energy Handbook- A Guide to Rural Energy Independence, Off-Grid and Sustainable Living” by William H. Kemp”, for further information on wastewater treatment systems.
- Wikipedia has an excellent discussion of gray water: http://en.wikipedia.org/wiki/Grey_water
- Berkey Water Filters
- This EPA site has everything you wanted to know and were afraid to ask about potable drinking water, sources, contaminants, etc.
- The National Sanitation Foundation (NSF) web site is: http://www.nsf.org/
- The American Water Works Association has issued standards for a number of materials use to treat drinking water. They also issue books on water treatment. Their web site is: http://www.awwa.org/
- Pamphlet 96: Sodium Hypochlorite Manuel This pamphlet is free from the Chlorine Institute: http://www.chlorineinstitute.org/ If you plan to use liquid hypochlorite be sure to get this pamphlet and follow it closely for handling, feeding and monitoring.