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Anions – ions (atoms or molecules with an electrical charge) with a negative (-) electrical charge, so named because they go toward the anode in an electric field. The main anions in water are hydroxide (OH -), carbonate (CO3-2), bicarbonate (HCO3-) (which together comprise “alkalinity”), sulfate (SO4-2), nitrate (NO3-) and chloride (Cl-).
Cations – ions (atoms or molecules with an electrical charge) with a positive (+) electrical charge, so named because they go toward the cathode in an electric field. Besides the hardness ions, the main cations in water are sodium, Na +, and potassium, K+.
Chloride, Cl- – a common mineral component, can be found in elevated levels near seawater and other salt supplies, which can cause taste problems and can contribute to corrosion. Recommended U.S. limit, 250 mg/L.
Color – the amount of brownish-yellow color from dissolved tannins from vegetation (like tea) and metals (like rust) and their combinations, measured on an arbitrary scale. The recommended maximum under U.S. regulations is 15 CU.
Conductivity – the relative ability of water to carry an electrical current, used to estimate the total concentration of dissolved ions.
Copper, Cu – cause of green stains on porcelain and fittings, seldom naturally-occurring, usually due to corrosion. The mandatory U.S. “actions level” of 1.3 mg/L is tied to the regulation for lead contamination due to corrosion of plumbing materials.
Fluoride, F- – often added to water to inhibit tooth decay. Mandatory U.S. limits range from 4.0 mg/ L in northern regions to 1.4 mg/L in southern regions (where more water in consumed).
Hydrogen Sulfide, H2S – a toxic, noxious, corrosive gas that smells like rotten eggs. Bacteria acting on sulfate or organic sulfurcontaining materials in the absence of oxygen produce it. Only “special” water analyses can determine hydrogen sulfide levels.
Iron, Fe – cause of metallic taste, rust stains on laundry and porcelain fixtures, and clogging/fouling of equipment. The recommended U.S. limit is 0.3 mg/L.
Manganese, Mn – cause of metallic taste and black stains on laundry and porcelain. Often occurs in combination with iron. The recommended U.S. limit is 0.05 mg/L Mn or a total of 0.3 mg/L of Fe + Mn.
Nitrate/Nitrite, NO3-/NO2- – important because of toxicity to infants, nitrate comes from fertilizers and animal wastes. Water supplies with high nitrate levels should also be screened for agricultural pesticides and bacterial contamination. The mandatory limit under U.S. regulations is 10 mg/L.
PH – the acid strength of water on a scale of 0 to 14 (neutral = pH 7.0). Values from 7-.0 are increasingly more acidic; values from 7-.14 are increasingly more alkaline. The recommended range for drinking water under the U.S. regulations is 6.5 to 8.5.
Silica, SiO2 – a naturally occurring dissolved mineral, which produces a glassy scale in high temperature equipment but is more important in predicting the life of certain water treatment media.
Sulfate, SO4-2 – a common mineral component, only rarely occurring at excessive levels, which can cause a temporary diarrhea in visitors who have not become acclimated to it. Recommended U.S. limit, 250 mg/L.
Turbidity – cloudiness in water caused by the dispersion of light by extremely tiny particles. Measured on an arbitrary scale of Nephelometric Turbidity Units (NTUs). The mandatory maximum under U.S. regulations is 0.5 NTU.
Total Hardness – the sum of all metal ions which react with soap to inhibit sudsing and form “scum” or “bathtub ring” – mostly Calcium and Magnesium. When heated or evaporated, hard water can cause lime scale that can deposit on sink and shower fixtures and walls and result in loss in efficiency or fuel waste in water heaters, boilers, and cooling systems.
Total Alkalinity – the sum of hydroxide (OH-), carbonate (CO3-2), and bicarbonate (HCO3-) ions, which can combine with both acids and bases, which act to buffer water and prevent sudden uncontrolled changes in pH .
Zinc, Zn – cause of metallic taste and upset stomach. Due to corrosion of galvanized plumbing materials. Recommended U.S. limit, 5.0 mg/L.
Units of Concentration
gpg-abbreviation for “grains per gallon” calculated in terms of calcium carbonate equivalents.
Multiply by 17.12 to convert gpg into
either ppm or mg/L.
ppm-abbreviation for “parts per million.” Interchangeable with mg/L.
mg/L-abbreviation for “milligrams per liter.” Interchangeable with ppm. (There are one million milligrams in a liter of pure water).
ppb-abbreviation for “parts per billion.” Interchangeable with μg/ L or micrograms per liter.
μg/L-abbreviation for “micrograms per liter.” Interchangeable with ppb. (There are a billion micrograms in a liter).
1000 ppb = 1 ppm; 1000 μg/L = 1 mg/L
RO Rejection Percentage= (Feed TDS – ProductTDS) / Feed TDS X 100