Q: I am an 80-year-old woman with osteoporosis, for which my doctor has prescribed a calcium supplement. He also suggested I take a single multivitamin every day, just to make sure I get all the nutrients I need. I drink between eight and 10 glasses of water a day, and a friend suggested that this could be causing the calcium and vitamins to flush out of my body without being absorbed. Is this true?

A: No. In the first place, the amount of water you consume can hardly be described as excessive, particularly if it represents your main source of fluid replacement. Besides the fact that it is essential to take in sufficient water to maintain fluid balance, generous amounts of liquids produce a dilute urine and may help to prevent urinary tract infections and kidney stones. Inadequate intake can lead to increased fluid absorption from the gut, which hinders bowel function.

Beyond these considerations, the amount of water-soluble nutrients that gets flushed out in the urine does not depend on the quantity of water you drink. It is affected first by the body's ability to absorb a particular nutrient, and second by how much you consume relative to how much your body needs. For example, if your body has as much riboflavin as it can store, the excess portion, whether absorbed from food or from a supplement, will be excreted in the urine.

Q; In a recent column you provided an interesting breakdown on the fat and protein content of various types of milk. Now can you tell me whether water is added as part of the procedure to reduce fat content? Also, how does the removal of fat affect the level of nutrients in the milk?

A: Reducing the fat content of milk is accomplished by simply skimming off the cream, not by adding water. The actual volume of fat replaced by the watery portion of the milk is small (only about 2 teaspoons per cup of milk). So there is just a minor rise in the amount of water-soluble nutrients in low-fat and skim milk. Reduced-fat milks with added nonfat-milk solids and, to a greater extent, those with enough milk solids added to be labeled "protein fortified," do have somewhat larger amounts of water-soluble nutrients.

Thus, a cup of whole milk provides 290 milligrams of calcium and .395 mg. of riboflavin, while a cup of protein-fortified low-fat or skim milk contains about 350 mg. of calcium and .475 mg. of riboflavin.

Vitamin A is reduced along with the butterfat, but under federal regulations it must be added to low-fat and skim milk that is transported across state boundaries. Many states have their own regulations for milk produced and consumed within their borders.

Last of all, vitamin D does not occur in appreciable amounts even in whole milk. But it is added to most milk sold in this country. The addition of both these fat-soluble vitamins (A and D) will be declared on the label. If you are using regular milk, it is a good idea to make sure vitamin D is added. And if you choose low-fat or skim milk, check to see that both A and D have been put in.

Q: Can you tell me why many commercial ice creams have stabilizers added to them?

A: Stabilizers are used both to promote the development of small ice crystals, essential for a creamy product, during freezing, and to maintain that creamy texture during storage.

Some small ice crystals melt even in the freezer. These water molecules then tend to unite with larger ice crystals, causing ice cream to become coarse. Vegetable bean gums such as locust bean, karaya and guar, as well as gelatin and sodium carboxymethylcellulose, are added to help ice cream and other frozen desserts withstand heat shock or temperature fluctuations that may occur, for example, on the trip home from the grocery store on a warm day. Apparently the stabilizer works by binding the free water, preventing it from depositing on existing crystals during freezing and storage.