HARDNESS - Calcium (Ca) and Magnesium (Mg)
The term hardness refers to the quantity of dissolved calcium and magnesium in water. These minerals, which come primarily from limestone type rock formations, are found to some degree in almost all natural waters. Calcium and magnesium cause problems for two principal reasons:
When the water is warmed, they precipitate out of solution and form a hard, rock-like scale. This scale accelerates corrosion, restricts flow, and reduces heat transfer in water heaters and boilers.
When they combine with soap, they react to form a curd, which interferes with cleaning, dries out skin, and leaves deposits on plumbing and clothes (bathtub ring; ring around the collar).
Hardness is measured in parts per million (or the equivalent mg/L) or in grains per gallon (gpg). Note: if the water analysis is given in ppm as CaCO3 then 1 gpg = 17.1 ppm. A common aspirin tablet weighs 5 grains). There is no established limit for the acceptable level of hardness in water, but is generally considered to become problematic at around 3 gpg.

Levels of hardness are referred to as follows:
Soft Water 0 - 1 grains per gallon (gpg)
Slightly Hard Water 1 - 3.5 grains per gallon (gpg)
Moderately Hard Water 3.5 - 7 grains per gallon (gpg)
Hard Water 7 - 10.5 grains per gallon (gpg)
Very Hard Water  over 10.5 grains per gallon (gpg)

Waters which naturally contain very little hardness can also be problematic because they may be corrosive in some applications (see acidity).

The only practical method for hardness removal above 15 gpg in residential applications is through cation exchange process employed by water softeners.

Acidity (pH)
Water which contains excess acidity tends to act aggressively towards plumbing and fixtures, causing corrosion and staining (ie. blue-green stains on fixtures from copper pipes). Relative acidity/alkalinity is measured on the pH scale, raging from 0 - 1.4, where 7 is neutral, numbers lower than 7 are progressively more acidic, and numbers higher than seven are increasingly alkaline (basic). The pH value refers not to the quantity of acidity, but rather to the relative acidity/alkalinity of a particular sample.

Alkalinity acts as a buffer to deactivate the acidity, a process called neutralization. For example, limestone (calcium carbonate) is often applied to soil to offset the acidity which comes from acid rain and decaying organic material. The accepatable range for water is 6.5 - 8.5. Acidity cannot be removed from water. However, it can be neutralized by raising the pH with alkalinity. This can be done by injecting a highly basic (alkaline) solution with a feed pump or by passing the water through a bed of processed limestone or similar material.

Iron (Fe)
The presence of Iron is a very common water quality problem, particularly in water from deep wells. Water containing even a significant quantity of iron may appear clear when drawn, but will rapidly turn red upon exposure to air. This process is called oxidation, and involves the conversion of ferrous (dissolved) iron, which is highly soluble, to ferric (precipitated) iron, which is largely insoluble. The ferric iron then causes red/brown staining of clothes, fixtures, etc.

Iron concentration is measured in ppm or mg/l (milligrams per liter, where 1 ppm = 1mg/l). Staining usually becomes a problem at concentrations greater than 0.3 ppm. Removal is through ion exchange (water softener) or oxidation/filtration (APIR).

Hydrogen Sulfide (H2S)
Hydrogen Sulfide is a gas which smells strongly like rotten eggs. It results from the decay of organic matter with organic sulfur and the presence of certain types of bacteria. Even very low concentrations are offensive as well as highly corrosive (silver tarnishes almost immediately upon contact with H2S).

Because it is in a gaseous form, H2S cannot be collected in a sample bottle for laboratory analysis. Therefore, its presence must be reported when a sample is submitted for treatment recommendation. Depending upon the test results, it can be removed by oxidation/filtration, aeration, or well sanitization.

Turbidity is a measure of suspended particles in water and can range from large particles which settle out of solution rapidly (such as sand), to extremely fine sediment which may stay suspended in solution even after standing for hours. Treatment depends upon size, which is measured in microns.

Tastes and Odors
Most tastes and odors are caused by the presence of organic matter and chlorine. The vast majority of these can be removed with activated carbon.

Total Dissolved Solids (TDS)
TDS is the sum of the mineral salts in water and if too high can result in objectionable taste, cloudy ice, interference with the flavor of foods and beverages and scale left behind in cookware. Generally speaking, the lower the TDS the more acceptable the drinking water. TDS of 1,000 ppm or more is unacceptable for drinking water. Reverse Osmosis (RO) process has proven itself as the most practical and cost effective method of correcting problems caused by high TDS.


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