You've been active outdoors all afternoon, and now you and your guests are back home for dinner. It's a festive, well-balanced Sunday meal. Dinner should be easy, because you began the preparation in the morning. You washed the green vegetable and left it soaking in ice water for crispness. You took the roast, bought at a very good sale price weeks ago, out of the freezer to thaw completely. The carrots, onions and turnips were peeled, cut up and left ready in the pot, and the potatoes peeled and left in water ready for heating. It's going to be a nutritious meal, not to mention tasty. But is it as nutritious as it could be?

Everyone thinks of nutrient loss of foods as part of harvesting, shipping and processing. But there are plenty of other ways right in the kitchen -- in the refrigerator, freezer and on the stove -- to lose vitamins and minerals. For example, soaking that green vegetable and potatoes in water caused a significant loss of water-soluble vitamins. The peeled and cut vegetables also were losing nutrients to the air from every cut surface, as well as losing enzymes that also went to work on the vitamins. Thawing the meat, which may have been necessary in the interest of haste, nevertheless resulted in a loss of nutrients, especially B vitamins and minerals into the juices.

Then, if you poured the cooking water for the potatoes and vegetables down the drain, instead of saving it for the gravy, even more vitamins and minerals went right along with it.

All in all, inept food handling and preparation can substantially subtract from the value of the foods we buy.

Since that's not just poor nutrition but poor economics as well, here are some guidelines on how to hang on to all the nutrients you've paid for at the supermarket.

The major concern is with the water-soluble vitamins - the B family and Vitamin C, and in particular with thiamin, Vitamin B-1 and Vitamin C -- as opposed to the fat soluble vitamins, A, D, E AND K. Tthe water-soluble vitamins are very vulnerable to heat, air and an alkaline medium, like baking soda.

First of all, there's the matter of storage. It's best to store fresh vegetables in plastic bags or the refrigerator crisper. although everything that is not peeled should be well-scrubbed before it is eaten, it's also better to leave the produce unwashed and untrimmed until you're ready to cook it. Fruits are best ripened at room temperature and then stored, uncovered, in the refrigerator.

Freezing will preserve the nutrients in fruits and vegetables for a longer period, provided they are first properly blanched, then packaged tightly and frozen quickly. The freezer's temperature should be kept at 0 degrees Fahrenheit (that's-20 degrees Centigrade).

Frozen vegetables should not be thawed before you're ready to drop them in the pot. If there is time, peel fresh vegetables just before cooking, or better still, leave the skins on and scrub them instead. The skins left on act as a barrier against nutrient leaching.

The best method of cooking is steaming, or bringing a very small amount of water to a boil before adding the vegetables. Keep the pot covered, cook only until the vegetables are al dente, and even though it's an old-fashioned practice, save the water for gravies, soups and stews. That, by the way, also goes for canned vegetables.

When you're making salads, remember that the dark outer leaves of green leafy vegetables and the outer layers of some others have the highest concentration of vitamins and minerals. That's also true of potatoes and the hulls or outer layers of most grains.

As for meats, fish and poultry, unless they are going to be used promptly, they are best frozen. Properly wrapped to prevent freezer burn and nutrient loss and kept at least at 0 degrees Fahrenheit, they can be stored for as long as three months without concern.

If possible, meats should be cooked without thawing, particularly if they are already cubed or chopped, so as to prevent losses of B vitamins and minerals in the juices. And, as with the cooking water from vegetables, the juices, skimmed of fat, can be used for extra nutritious soups and gravies.

Methods of cooking also affect the retention of nutrients. Broiled meats, for example, generally retain between 60 and 80 percent of their thiamin. Again as with vegetables, the water or stock used to braise or stew will leach nutrients from the meat, while oven cooking or broiling is less likely to produce as much loss.

What about foods kept on the shelf for longer periods? For maximum vitamin retention, canned fruits and vegetables should be kept in a cool place -- that is, at 65 degrees Fahrenheit or below.

Finally, if you're storing leftovers, cover them tightly, keep them cold and reheat only the amount that can be used at one meal. With these simple tricks, you not only will save on money but on flavor and nutrition as well.