Magnesium carbonate (magnesite) and necessary, authorization must be obtained from magnesium bicarbonate. Act the same in water as calcium carbonate and bicarbonate.

Magnesium sulfate (epsom salts). Adds to the noncarbonated hardness of water and causes boiler scale. In amounts greater than 500 parts per million in drinking water, it acts as a laxative. .

Magnesium chloride. Has the same properties and effects as calcium chloride. However, the magnesium will contribute to the formation of magnesium hydroxide scale on boilers and evaporators. .

Iron. Iron is undesirable because it imparts a rusty color and objectionable taste to water. It also forms crusts in plumbing and piping. When iron is present in water, organisms whose life processes depend on iron compounds may also be present. These organisms may cause tastes and odors and create what is called red water.

Manganese. While not encountered as often as iron, it is found in both surface and ground water. Its presence in water normally causes a grey or black color. The total concentrations of iron and manganese in potable water should not exceed 0.3 ppm.

Iron and manganese removal is not normally required in the production of field drinking water. Oxidation by aeration, followed by sedimentation and filtration, is the most common method of removing iron and manganese. They are oxidized to insoluble ferric oxide and manganese oxide by this process. The same methods may generally be used to remove both iron and manganese, although when they are present together in water, removal is more difficult. Combinations of iron and manganese with organic matter may require aeration in trickling beds containing coke, followed by sedimentation and filtration. In some cases superchlorination followed by sedimentation and filtration will in itself remove these two substances. The addition of lime, Ca(OH)2 , followed by sedimentation and filtration, is another method for removal of these substances.

The concentration of chemical substances present in water for military water supply should not exceed the values shown below. If local conditions or short-term requirements make the use of water containing higher chemical concentrations the medical officer.

Chemical Substances Maximum Values

Copper . . . . . . . . . . . . . . 1.0 ppm

Iron . . . . . . . . . . . . . . . . 0.3 ppm

Manganese . . . . . . . . . . . 0.05 ppm

Zinc . . . . . . . . . . . . . . . . 5.0 ppm

Magnesium . . . . . . . . . . 125.0 ppm

Chlorides . . . . . . . . . . . . 250.0 ppm

Sulfates . . . . . . . . . . . . . 250.0 ppm

Phenolic compounds . . 0.001 ppm

Lead . . . . . . . . . . . . . . . . 0.05 ppm

Hexavalent Chromium . . . . . 0.05 ppm

Fluoride . . . . . . . . . . . . . . . . . . . 1.5 ppm

Turbidity (silica scale) . . . . . 5.0 units

Color (platinum-cobalt scale) . . . . . . . . . . . . . 15.0 units

Nitrate-Nitrogen . . . . . . 10.0 units

Total solids 500.0 ppm

Water softening is the term used to identify the process of treating water supply hardness. Water softening is most likely to be necessary when water is being supplied to laundries and heating units involving boilers and steam equipment.

Lime - Soda Process. Lime-soda ash softening consists of the application of these materials to the raw water. Lime, Ca(OH)2 , reacts with the soluble calcium and magnesium bicarbonates and forms insoluble calcium carbonate and magnesium hydroxide. Soda ash, Na2 CO3 , reacts with the soluble noncarbonated compounds of calcium and magnesium to precipitate insoluble calcium and magnesium compounds but leaves sodium compounds in solution. The physical operation of adding lime-soda ash and removing the precipitates is similar to that in the conventional coagulation-filtration process for bacteria and turbidity removal.

Zeolite Process. Zeolites used in water softening are complex compounds of sodium, aluminum, and silica which have the faculty of exchanging bases. They are often called green sand because of the color of natural zeolite.

Synthetic zeolites are also available. When water