Creating a cost effective in-home water purification system

Water is a life giving and sustaining resource. Its purist form is when distilled and all impurities have been removed, its purist natural form is rain water from a non polluted atmosphere. Unfortunately, the atmosphere in most cases is polluted and once the rain water hits the ground many more pollutants contaminate it.

 

In addition to metallic, chemical and organic pollutants found in the air and in the ground there are biological pollutants such as viruses, molds and fungi. In combination these pollutants can cause a number of problems for house hold occupants and the systems we use in our homes that distribute and use water.

 

The water that arrives at our homes in Prescott Arizona has been contaminated with a number of organic, biological chemical compounds, contaminants that change water properties. The most obvious is the injection of disinfecting chlorine and what is known as hardness in water. Rain water in its purist form, that is no contaminants, is considered soft water; however, on its way to our homes groundwater dissolves rocks and minerals that release calcium and magnesium ions that cause water to be hard. The Term 'hard water' comes from the type of deposits that are left behind when the water evaporates leaving residue known as scale.

 

These scale deposits are composed mainly of calcium carbonate, magnesium hydroxide, and calcium sulfate and tend to be deposited as off-white solids on the surfaces of pipes. When heated these compounds are residue from the water through evaporation and produce a scale buildup on hot water heater elements. A large scale buildup slows the heating process and requires more energy to heat the water; it over heats the units heating elements and shortens life span. Scale deposits also corrode and plug plumbing fixtures and accumulate in other water appliances affecting their performance.

 

Hard water also interferes with all types of cleaning tasks. Regular soaps combine with dissolved calcium and magnesium to form a white precipitate of soap scum instead of producing lather; scum that is difficult to remove from sinks and appliances. Cleaning problems also arise when the cleaning agents do not fully remove dirt and grime. Over time, clothes washed in hard water may look dingy and feel harsh and scratchy. Dishes and glassware washed in dishwashers using hard water may be spotted when dry. Hard water also causes films on glass shower doors, walls and bathtubs; and has an adverse effect on hair and skin.

 

Water hardness is ordinarily expressed in grains of hardness per gallon of water (gpg), but can also be measured in either parts per million 'ppm' or milligrams per liter 'mg/l'. In Prescott the grains of hardness are between 6.6 and 7.4 gpg and between 113 and 127 ppm.



From the table below it can be seen that Prescott water is positioned right between moderately hard and hard.

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Level of Hardness in grains 'gpg'
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Below 1.0 soft     
1.0 to 3.5 slightly hard      
3.5 to 7.0 moderately hard    
7.0 to 10.5 hard     
Above 10.5 very hard     

 

For reasons highlighted above and the high level of hardness in Prescott water it was decided to install a water softener. The main purpose of the softener being to counteract the negative effects of hard water by taking nearly all the calcium and magnesium from the raw water during the softening process.



The advantage of the softening process is longer life of appliances including washing machines, dishwashers, and water heaters; less use of household cleaning products such as detergents, as well as personal care products, like shampoo; a reduction of water spotting and cleaner softer feeling clothes.

 

Water softening is often recommended to soften only the water sent to domestic hot water systems. However, it is also important that cold soft water be sent to cleaning appliances such as clothes washers, dish washers and washing faucets at sinks and showers.

 

The next action was to select an appropriate softener solution. There are a number of softening technologies and a number of manufactures; all who believe theirs is the best. The top two softener technologies are salt-based systems and non-salt systems.

 

  • Salt based: Uses an ion exchange procedure to remove calcium and magnesium.

 

  • Salt free: Softeners harden the calcium into minute particles that are said to be washed away with waste water.

 

SALT-BASED WATER SOFTENERS (ION EXCHANGE)

 

Calcium and magnesium ions that cause water hardness can be removed by using an ion exchange procedure.  Salt-based water softeners use sodium or potassium as the exchange ion.  Sodium ions are supplied from dissolved sodium chloride salt, also called brine.  As hard water passes through a softener, the calcium and magnesium trade places with sodium ions.  After softening a large quantity of hard water the exchange medium becomes coated with calcium and magnesium ions.  To recharge the softener it is back flushed with a salt brine solution that replaces the calcium and magnesium ions on the exchange medium.  The time between recharging cycles depends on the hardness of the water, the amount of water used, the size of the unit, and the capacity of the exchange media to remove hardness. All these parameters must be considered when sizing a system. There are a number of on-line calculators for sizing systems; the one used here is at http://www.apswater.com/Water_Softener_Calculator.asp. Based on the calculations our system for 3 people using 40 gallons of water a day (based on water bills) and two bathrooms required a 32,000 grain system that required a backwash every 18 days.

 

While softened water from a salt-based water softener is truly softened and highly efficient it is not recommended for drinking, or watering houseplants, lawns and gardens due to its sodium content. For people on a low-sodium diet, the increase in sodium levels in the water can be significant, especially when treating very hard water.

 

SALT-FREE WATER SOFTENERS (CATALITIC MEDIA)

 

Salt free units use a catalytically working filter media in a process where atoms are placed in a special structure so that an active surface is created.  It transforms the dissolved calcium carbonate so it cannot attach to any surfaces.  The chemical bonds are then rinsed away by the water flow. 

 

The non-salt solutions claim is that they isolate the calcium without the use of salt or potassium and require no chemicals, electricity, or back flushing to operate.  There is no wasted water or drains to install and it is environmentally friendly.

 

However, there are a number of reports concerning the efficiency of non salt systems. Only salt-based water softeners “soften” water. Systems that work without salt, “condition” the water by preventing it from sticking to any surface and although these systems work to some degree, none to my knowledge have passed the eighty percent efficiency requirement of the DVGW-12 standard. The hard water components are still present in the water after conditioning and a number of the original hard water issues are still present; for example, residue is still apparent on glasses and glass doors when the water evaporates.

 

After analyzing a number of the salt-free unsubstantiated claims and negative feedback from a number of blogs, a conventional salt based system that had a proven track record for efficiency, reliability and cost was selected. However, the softener was bypassed for drinking and cooking use.

 

Hard water is just one aspect to an efficient in-home water filtration system; the removal of bad taste and chlorine odor and harmful chemicals is also essential. Chlorine added by most water authorities to help disinfect ground water during storage and distribution has a number of bad effects on water and water appliances; primarily the water tastes bad and has an obnoxious odor, and secondarily it stains sinks, toilets and other water using appliances and it saturates water filters.

 

After analysis a simple in-line home sediment and chlorine filter was placed before the soft-water system. This particular system supports a seven gallon per minute flow rate and a filter life of 150,000 gallons. In a typical home with four people using 80 gallons a day the life of the filter would be around one and a half years. In our case at 40 gallons a day and two people around five years. It will also remove a number of contaminants before entering the water softener and therefore extend its life considerably.

 

The final stage of an integrated water filtration system is the drinking water unit. This unit has to filter all the other containments that can harm human health. We have passed the incoming water through the sediment and chlorine filter so these chemicals will not overwhelm the under-sink and refrigerator water filter; even though most under-sink filters also filter for sediment and chlorine.

 

The unit chosen was a multi-stage unit designed to filter a number of different contaminants. The first stage removed volatile organic carbon compounds (VOC's, insecticides, pesticides and industrial solvents). The second removed suspended particles such as silt, sediment, microscopic parasites (Giardia, Cryptosporidium), sand, rust, dirt, and other un-dissolved matter. The water then flows through an electro-chemical and spontaneous-oxidation-reduction alloy that removes heavy metals such as lead, mercury, copper, nickel, chromium, cadmium, aluminum, and other dissolved metals are removed from the water by an electrochemical process. The media also inhibits bacterial growth (fungi, algae and mold) and reduces lime scale, mold, and fungi throughout the entire unit.

 

Granulated activated carbon (GAC) is universally recognized and widely used as an effective adsorbent for a wide variety of organic contaminants, such as chlorine, chemicals linked to cancer, pesticides, herbicides, insecticides, volatile organic compounds and hundreds of other chemical contaminants that may be present in water.

 

This particular unit uses a high-grade coconut shell carbon that is most effective at removing chemicals. Coconut shell carbon provides a significantly higher volume of micro-pores; as a result, it is more effective than other carbon types in removing trihalomethanes and other chemicals from municipally supplied water.

 

Since the in-line chlorine filter selected removes the chlorine before it reaches the carbon in this system, the carbon capacity is not wasted on chlorine and is free to concentrate more effectively on the other organic contaminants.

 

In the final stage,water flows through another one-micron filtration pad for further reduction of undesirable particles. The end result is a great reduction or elimination of a wide variety of contaminants. In Prescott Arsenic is a concern as it is at a relatively high level of 8.7ppb the selected filter system reduces Arsenic by 98%


The chart below highlights the number of contaminants and the efficiency by which they are removed by the GAC filter elements.

 

Test Results at 20,000 Gallons

Chemical

Influent

Effluent

Efficiency

EPA MCL

THM (chloroform)

0.57

0.029

95%

0.1

Lead

0.19

0.006

97%

0.025

Fluoride

8.26

0.78

91%

1.4

Nitrate

30.7

8.03

74%

10.0

Barium

10.4

0.56

95%

1.0

Arsenic

0.37

0.007

98%

0.05

Cadmium

0.03

0.004

87%

0.01

Chromium VI

0.15

0.011

93%

0.05

Chromium III

0.163

0.003

98%

0.05

Selenium

0.1

0.006

94%

0.01

Mercury

0.006

0.000*

99+%

0.002

Endrin

0.0008

0.000*

99%+

0.0002

Lindane

0.011

0.0012

89%

0.004

Methoxychlor

0.32

0.0059

98%

0.1

Toxaphene

0.013

0.000*

99%+

0.005

2,4-D

0.3

0.02

93%

0.1

Silvex (2,4,5-TP)

0.029

0.004

86%

0.01

 

So in conclusion we have selected three systems the first removes general sediment and chlorine from the incoming water, the second softens the water for all the heating and cleaning appliances and the third provides contaminant free drinking and cooking water.

 

Another very important factor during the evaluation was cost. A number of systems, many of which only provide partial filtration, are relatively expensive ($2500.00). The system described above cost less than $1000.00

The final activity was outlining the overall architecture to the installing plumber. The first priority for the incoming water supply is for it to be piped to the outside bibs for landscaping, as plants and trees need all the complexities of unfiltered water. All internal water usage should have the sediment and chlorine removed, so the in-line chlorine unit comes next followed in parallel by the soft water system for the hot and cold water appliances, showers, toilets and sinks, and the kitchen drinking water unit to the sink for drinking and cooking and the refrigerator for drinking and ice.

 

My thanks to Fleck water softeners, Affordable water, filters4h2o, Crystal Quest and the city of Prescott for providing content for this article. The systems chosen for this project were the Fleck 5600SXT 32K grain salt-based softener; the HVFMX1CS chlorine system from filters4h2o and the Crystal Quest Mega double under-sink filter system.