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Current IssueOctober 24, 2014
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Ask The Expert: Practical or aesthetic effects of both low or high pH
02/01/2008 
 
Question:

I have read extensively on what pH is and understand as much as my high school education will allow; however, what I need to know is what are the practical or aesthetic effects of both low or high pH?

Larry Say: aquaboss@embarqmail.com

 

Answer: 

I have read extensively on what pH is and understand as much as my high school education will allow; however, what I need to know is what are the practical or aesthetic effects of both low or high pH?

Larry Say: aquaboss@embarqmail.com

pH is a measure of acidity and alkalinity in water. Neutral is pH=7.0, meaning that the acidity and alkalinity are exactly balanced. Lower pH means acid. Higher pH means alkaline. The acceptable pH range for potable water is 6.5 (slightly acidic) to 8.5 (slightly alkaline). Acidic water tends to be corrosive and will react with plumbing, putting metals into the water and affecting taste (bitter). Alkaline waters tend to be more prone to forming scale and also have an off taste. Most tap waters are delivered between a pH of 6.8 and 8.2.

C.F. 'Chubb' Michaud, C.E., CWS-VI, Systematix

A water pH below about six is pretty acidic and will tend to dissolve certain piping (e.g., black iron andcopper), causing staining of fixtures. Although taste is subject to personal interpretation, this acidic water may taste sour, like lemon juice. Water pH above nine or so will readily cause scaling of fixtures and have an alkaline taste, perhaps like milk of magnesia.

Peter S. Cartwright, PE, Cartwright Consulting Co.

The NationalSecondary Drinking Water Regulations for pH established by the United States Environmental Protection Agency (US EPA) limits pH value between 6.5 to 8.5 primarily for its affect on the aesthetic quality of drinking water. The pH value indicates the intensity of alkalinity or acidity just as temperature indicates how hot something is but not how much heat the substance carries. Numbers below seven are considered acidic andnumbers above seven are considered alkaline. pH stands for potential of hydrogen and is the symbol our industry uses to determinethe degree of acidity or alkalinity of a solution. In technical terms, pH is expressed as the logarithm of the reciprocal of the hydrogen ion concentration in gram equivalents per liter of solution. Distilled water is regarded as neutral with a pH of seven or 0.0000001 gram atom of hydrogen ion per liter. That said, one of the most important factors when obtaining an accurate water analysis is a true pH reading. Transporting a sample for testing should be avoided at all times because atmospheric exposure will allow adjustment of low pH to a non-corrosive state of equilibrium. The only exception would be collecting the raw water in specially prepared sample jars for a laboratory analysis. Even then, time is of the essence considering the water should be kept chilled and tested within 30 hours for the most accurate lab report. Effects of low pH must be given serious considerationsfor several reasons. First, low pH is largely influenced by the presence of carbon dioxide (CO2) which, when ionized in aqueous solution, creates carbonic acid that is very deleterious to metallic components of a typical domestic residential service plumbing system. Low pH is easily identified by blue/green stains on the fixtures and solidified deposits on aerators, shower heads and hose bibs. Secondly, an analysis of the water after it has been in contact with copper piping will usually yield a significant increase in the total copper level relative to the influent stream. It is vital to correct this offending condition in the water to stop the degradation of the plumbing and staining of the fixtures. Finally, there may be health related issues if the copper levels test at the action level or above the maximum contaminant level (MCL) established by the US EPA. Several methods are available for pH correction. The most popular is an acid neutralizing media blend that elevates low pH when exposed to the free carbon dioxide by releasing calcium carbonate and magnesium oxide into the water as hardness. In most cases this will significantly reduce or stop the corrosion as well as leaching of copper and other metals into the water. Effects of high pH can be bad for the opposite reason. Hard water is problematic in that it quickly forms scale that is evidenced by crystalline formations on the aerators, shower heads and hose bibs. Additionally, the heat transfer surfaces of boiler tubes, gas water heaters and heating elements in electric water heaters accumulate energy-robbing scale build up. Imagine a layer ofbricks stacked on your stove and thentrying to heat your tea pot through the bricks. Instead of correcting a corrosive (low pH) condition in the water, it is necessary to correct the scaling problem created by the hardness in the water. Ion exchange water softening is the most recognized and cost-effective method for removing hardness from water, which in turn significantly reduces this scale problem As you can see here, Larry, the aesthetic quality of water in most cases can be attributed to the pH value of the water under consideration and therein lies the practicality of never losing sight of the need to ascertain with certainty the real pH value of the water to isolate the root cause of any water problem.

Gary Battenberg, Hague Quality Water International

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