Off Grid Water Part 3 – Home Water Treatment Devices

By Off Grid Ebert

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 III. Home water treatment devices. What exactly do they do and, more importantly, what don’t they do!

Primarily, because of the perception by significant number of people that municipal water is not acceptable when coming out of the tap there are thousands of water devices and treatments marketed to the general public.

Starting in 2003, there were NSF¹ standards established for certification for most water treatment devices. These performance standards have been revised several times since. Confirm that any device you are considering buying and installing has the NSF performance certification.

Most water sources require some pretreatment before use for potable drinking water. Some of the most common conventional treatments, typical performance specifications, and limitations are listed in the following table.

Caution: There are numerous black boxes that are sold to treat potable drinking water. Before buying one determine which of the following types of treatments are being used. Likely one or more are claimed to be included in the device. If the treatment method, capabilities, limitations, service and/or maintenance cost is difficult to understand or confusing you may be sold a device that either does not work as claimed or there will be expensive to service or expensive replacement parts required. Be very careful that you understand it and that it’s function is based on sound proven physics and/or chemistry principle before buying and installing it!

Device or Treatment	Typical Performance Specifications	Limitations	Comments
Settling, for example, a pond or other holding area with long retention time.	Varies widely but should remove most suspended solids	Does nothing to remove bacteria, algae or viruses. Fish, birds and wild life are possible problems	Economical if land is available
Granulated Activated Carbon (GAC)_Filtration	Removes trace organics and oxidants	Usually, must be after filtration and/or clarification. Does not remove hardness. Will destroy chlorine and other oxidants.	Often source of bacteria, can change pH of water to acidic in low carbonate waters
Clarification	Similar to filtration except usually uses a large concrete or steel basin. Removes most suspended solids	No removal of hardness. Must be sized and operated correctly	Usually requires coagulant and/or flocculants
Air Oxidation	Will convert all soluble iron to insoluble iron and some of manganese	Will not quantitatively oxidize manganese or sulfide	Requires specific equipment and pump
Sand Filtration*	Removes most suspended solids	Does not remove bacteria or anything less than 10 microns	Backwash can be an issue. Potential Bacteria source
Mixed Media Filtration*	Removes most suspended solids Less subject to fouling	Similar to sand filter	More expensive than a sand filter. Potential bacteria source
Ultra Fine Sand Filtration*	Removes all suspended solids down to ~ 1 micron. Low backwash	Patented design to avoid fouling	Only available from a few sources. Claimed to remove bacteria
Centrifugal Filter*	Will remove suspended solids down to around 30 micron		Can be source of excess backwash if on timer.
Gravity Filter*	Removes most suspended solids but depends on media	More subject to fouling compared to up flow filters	Up flow filters have less fouling potential
Cartridge Filter*	Removes virtually all suspended solids	Requires manual replacement.	Can used to remove solids, or hardness or iron
Sodium Zeolite Softening	Removes virtually all Calcium and Magnesium	Does not change conductivity. High iron/manganese may require chemical treatment to avoid fouling	Sodium level in water increases. Will remove iron and manganese
Demineralizer	Removes all dissolved ions	Requires filtration before demineralization	Requires acid and caustic for regeneration
Distillation	Removes all dissolved solids	Does not remove carbon dioxide	Requires high energy.
Reverse Osmosis	Removes virtually all dissolved ions down to about 30 MW.	Requires pre-filtration, GAC to remove oxidants, and requires high pressure pump	Expensive, extremely subject to fouling from silt and bacteria
Green Sand filter	Removes most of iron and manganese	Can be source of Manganese and iron!	Requires nasty Permanganate for regeneration
Alum (aluminum sulfate)	Coagulant aid to remove suspended solids	Acidic precipitate has a lot of water associated with it.	Sludge disposal can be a concern and costly because of high water content
Sodium aluminate	Coagulant aid to remove suspended solids	More expensive than alum but has less impact on pH compared to alum
Polyphosphate	Reduces hardness, binds soluble iron and manganese and reduces corrosiveness of water.	Requires feed system	Only 1-3 ppm required. Prohibited in great lakes area
Zinc	Corrosion inhibitor for soft water	Prohibited in coastal, brackish or salt water areas	Human and bacteria nutrient; only requires a trace residual.
Silica	Used for corrosion inhibition	Very complex, unpredictable chemistry	Rarely recommended
Polyacrylate (polymers)	High Molecular Flocculant used with coagulant	Specific MW based on size and charge of suspended solids	Reduced volume of sludge compared to alum or aluminate
Poly Aluminum chloride	Primary coagulant		Reduces sludge volume and disposal costs compared to alum
Liquid Chlorine-sodium hypochlorite Usually sold as 12%.	Broad spectrum biocide; easy to monitor; easily controlled by free residual test	Poorly effective towards some multi-cellular organisms and some viruses; must not be used with water that contains significant lignin and tannins because of trihalomethanes (THMs) production	Is “basic” alkaline, therefore must be carefully handled and fed.
Hydrogen Peroxide	Broad spectrum oxidant biocide	Quickly decomposes; no residual	Very difficult to safely handle and feed
Ozone	Extremely strong broad spectrum oxidant biocide	Primary pollutant in urban areas. Must be carefully applied. Expensive to operate and requires costly electrode replacement	Probably will be banned by the EPA in the future. Not appropriate for most domestic use.**
Ultra-violet radiation	Can be effective. Two wave lengths available.	Water must be free of suspended solids. Requires high voltage, clean tubes and long exposure time to be effective.	Not appropriate for most domestic use.**
Chlorine Dioxide	Strong broad spectrum oxidant biocide	Requires generator and chemicals.	Not appropriate for domestic use**.

*All filters ideally should be equipped with pressure gauges, a flow meter, and sample points (before and after) to assess their performance. Treatment of backwash water with an oxidizing biocide is recommended to enhance and extend the filter performance time between back washings and to prevent the filter from becoming a major source of bacterial contamination. Because of reduced fouling up-flow filter design is preferred.

** These are the author’s personal opinions. Others may disagree.

¹The National Sanitation Foundation (NSF) Certification Program website is:

http://www.nsf.org/consumer/drinking_water/dw_treatment.asp

See our Berkey Water Filter review for home-use filtration without electricity.