The sodium ion, being the sixth most abundant metallic ion in the earth's crust, is a natural constituent of both food and water. In nature we find sodium in water from several sources. These are:

• Underground sodium salt deposits which are dissolved by water
• Sea water
• Natural ion exchange in soils where calcium ions in the water are replaced with sodium ions.

Sodium occurs naturally in foods because plants take up sodium from the soil water, and animals ingest plants and water containing sodium.

Man adds sodium to food and water in various ways. Sodium is added to water during the following processes:

• Water purification and bacterial control in water supplies are accomplished by adding sodium hypochlorite.
• The lime-soda method of softening water in municipal water treatment plants requires the addition of sodium compounds such as sodium carbonate.

Man adds sodium to food for a variety of reasons. Sodium compounds are added to improve the flavor of many foods. For example:

• Sodium chloride (salt) and monosodium glutamate (MSG, Accent, etc.) are used by com­mercial food processors in bacon, salted crackers, olives, soups, sauces, and almost all convenience foods such as frozen dinners and packaged mixes. These two products are also ad­ded by the homemaker in home food preparation.
• Sodium compounds are also used to improve the tex­ture of some foods.
• Sodium bicarbonate in baking soda and baking powder makes baked goods rise.
• Sodium alginate is used in chocolate milk and ice creams to improve their texture.
• Sodium hydroxide is used to soften the skins of olives, certain fruits and grains.
• Sodium compounds are used to preserve some foods. Sodium benzoate is used in jellies, relishes, and salad dressings.
• Sodium propionate is used to inhibit mold growth in cheeses and bread.

Sodium compounds are also used in many common medications such as:

• Baking soda (home remedy for indigestion), and sodium compounds are used in many alkalizers and antiacids as well as many headache remedies, sedatives, and cathartics.

It is estimated that the average person consumes the equivalent of 2 to 3 teaspoons of salt per day from all sources. This is about 8 to 15 grams. Some of this salt is in the food naturally, but most of it is added in processing, preservation, cooking, and at the table. A salt (sodium chloride) intake of 8 to 15 grams is equal to about 3 to 6 grams (3,000 to 6,000 milligrams) of sodium.

Since sodium is added to water softened by the cation exchange process (mechanical water softening), the level of sodium in softened water may be of interest to persons on sodium restricted diets.

The table below shows the amount of sodium added to softened water of varying original hardness. The harder the water originally, the more sodium that is added.

Assuming a daily intake of 5 grams (5,000 milligrams) of sodium in food and the consumption of 3 quarts of water (used for coffee, tea, food preparation and drinking) the contribution of the sodium (Na+) in the water from the home water sof­tening process compared to the total daily intake can be seen in the following table:

Persons who must restrict their sodium intake to 500 milligrams per day should consume water that con­tains no more than 20 milligrams of sodium per quart. This is assuming that most people consume about three quarts of water per day from all sources (beverages, food preparation, and drinking). 20 milligrams per quart X 3 quarts = 60 milligrams total daily from water.

The 60 milligram level has been suggested since the basic 500 milligram therapeutic diet actually con­tains about 440 milligrams of sodium from food. This allows 60 milligrams of sodium from water.

If sodium (Na+) is restricted to 1000 milligrams per day, the upper limit for total sodium content of water is about 200 milligrams or about 66 milligrams per quart if three quarts are consumed.

See the following table for original hardness limits of softened water for different levels of water consumption.

If an ion exchange water softener is to be used in a home where a person is on sodium-restricted therapy and water hardness is great enough that excess sodium may be consumed by using softened water, a by-pass can be installed to provide unsoftened water for drinking and cooking.

In some localities the sodium content of the municipal water supply and water from wells may also be higher in sodium than can be allowed.

Persons on sodium-restricted therapy can obtain ad­vice from a physician or dietician. The municipal water department will provide a detailed analysis of the water supply.

Detailed analysis of well-water can also be obtained. Contact the municipal water department, the Public Health Service, a local water softening dealer, or the Cooperative Extension Ser­vice for the name and address of a laboratory which makes this analysis.

Information compiled by Jerry Rivers, PhD Professor Human Nutrition and Food, New York State College of Human Ecology, Cornell University, Ithaca, New York.