DISEÑO E IMPLEMENTACIÒN

Plain drinking water from the tap isn’t so plain. As we have seen, water is a superb solvent, so de- pending on where it’s been, substances of all kinds dissolve in it. Even rain water falling through clear air collects various gases before it hits the ground. The dissolved substances are what give various waters their distinctive tastes—and some- times odors and colors—and are what determine whether or not the water is safe to drink.

Although our senses separate the good-tasting from the bad, they don’t necessarily tell us which water is safe and which isn’t. For example, drink- ing water rich in iron tastes and smells bad, but iron is safe to drink. But lead in the drinking wa- ter, even at toxic levels, is tasteless and odorless.

For the nation as a whole, lead is the pollutant of most concern in the drinking water. The developing nervous system is particularly vulnerable to the toxic effects of lead. Thus, lead exposure is most worrisome among pregnant women and young children—population groups that also tend to be low in iron and calcium. Diets rich in iron and calcium can lessen the amount of lead absorbed.

Progress is being made in reducing this source of lead. The amount of lead allowable in drinking water has been lowered, and water suppliers are required to notify customers of any lead in the water. Also, current safety regulations ban lead pipes in new plumbing to be used for drinking water. Homes more than 100 years old might still have lead pipes, which should be replaced.

Lead solder on pipes is less serious (but more widespread), especially if the solder is more than 5 years old (lead solder dissolves more easily dur-

ing the first 5 years). If your household plumbing is suspect, the water can be tested, and local water departments usually offer advice and help.

From 2007-2010, about 2.6% of U.S. children ages 1-5 had blood-lead levels of more than 50 ppb. Even levels below this can cause cognitive and behavior- al problems; no safe level of lead has been estab- lished.4 _{Environmental sources of lead include lead}

in housing, soil, water, and consumer products. Children often ingest flakes or dust from old peeling lead-based paint (directly or through contamination of other things they put in their mouth).

Despite the variations in tap water throughout the country, most drinking water from the tap is safe, especially when the water comes from large municipal water systems. Any lead contamination generally comes from the lead in plumbing. Other hazardous contaminants tend to be localized (e.g., water from wells in certain areas).

Another aspect of drinking water to consider is its fluoride content and whether the water is “hard” or “soft.” Fluoride is found naturally in water and hardens the enamel of developing teeth, making the teeth highly resistant to tooth decay. (Fluoride in the drinking water also may possibly strengthen bones, offering some protection against osteoporosis.)

The optimum level of fluoride is about 0.7 ppm (0.7 part fluoride per million parts of water), a level which protects against tooth decay but isn’t enough to produce [harmless] mottled tooth enamel. Some water supplies naturally have more (and some fluoride can be removed); other water supplies need added fluoride to reach this level.

Whether water is “hard” or “soft” depends on its content of calcium, magnesium, and sodium. Hard water is relatively high in calcium and magnesium, and low in sodium, whereas soft water is relatively high in sodium and low in calcium and magnesium. Unlike soft water, hard water leaves behind a hard [mineral] “scum” or deposit in the automatic coffee maker, bathtub, etc., and interferes with the action of various soaps. Soap doesn’t “suds up” as well in the shower or dishpan, and hard water “grays” the white laundry.

So, many households prefer soft water. Some households install a water-softening apparatus to convert hard water into soft water (the apparatus

Part 5. Fueling the Body

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exchanges the calcium and magnesium in the hard water for sodium). But because soft water is high- er in sodium, this can be a concern for those on sodium-restricted diets. Also, soft water is slightly acidic, making it somewhat corrosive. (If there’s lead in the plumbing more of it will dissolve in soft water than in hard water.) A compromise is to soften only the hot water supply, and use only the cold (hard) water for drinking and cooking.

Bottled water is exceedingly popular. There’s a large variety—flavored or unflavored, with or with- out minerals, carbonated or not. Although many people drink bottled water simply because they like the taste, many drink it because they perceive it as more healthful than tap water. This perception is certainly valid if the tap water is harmfully contaminated, but this isn’t usually the case.

If your tap water doesn’t meet the standards of the Environmental Protection Agency (EPA), the water company is required both to notify you and to clean it up. The standards set for bottled water aren’t necessarily higher than for tap water, and most of the bottled water sold in the United States is in fact processed tap water.

Besides the added cost, an argument against bottled water is environmental, e.g., energy and pollution costs of bottling and transporting the bottles. Also, bottles that aren’t recycled contribute to the plastic debris that litter our land and sea.

Bottled water sometimes can be less health- ful than tap water. Some, for example, are comparatively high in sodium. The various types and brands of bottled water can be confusing to the consumer. Although the brands vary and the types overlap, a few generalizations can be made:

Distilled water: Water is evaporated to steam,

and the steam is condensed to make distilled wa- ter. Thus, the solid, mineral matter (including sodium) is left behind. (The distillation process doesn’t, however, remove all organic chemicals.) Since minerals give water their taste, distilled wa- ter tastes flat.

Mineral water: Water that contains minerals—

which includes virtually all water except distilled water. Most bottled mineral water is, however, taken from a spring, and afterwards the mineral content of the water may or may not have been

altered. When it’s called “natural mineral water,” its mineral content hasn’t been altered.

Spring water: Simply water that comes from a

spring. It may or may not have been processed and, as ground water, it may or may not be contaminated. “Natural spring water,” means that it hasn’t been processed before bottling.

Sparkling water: Water that’s naturally or artifi-

cially carbonated. It tends to be relatively high in sodium.

Seltzer: Usually tap water that has been filtered

and carbonated. Often, flavors are added, and sometimes sugar is added as well.

Club soda: Like seltzer, usually tap water that’s

been filtered and carbonated. But unlike seltzer, minerals (usually including sodium) are added.

Summary

Water is an important nutrient that’s often overlooked in discussions of diet and nutrition. Yet our bodies are more than 50% water, and unlike the other nutrients, we can’t survive more than a few days without it. Water works by acting as a solvent, allowing chemical reactions to take place, and also takes part in many of our biochemical reactions.

Our bodily water is both intracellular and extracellular, constantly moving, along with other dissolved substances, in and out of our cells. The amount of water in an adult body is inversely related to the amount of body fat. Also, when we lose muscle mass (as in aging), we lose the water that’s in that muscle.

Some of our body water can be lost or gained relatively quickly, from things like water intake, hormones, sodium, diuretics, exercise, and diet. Much of the quick weight loss that occurs within a few days of starting a diet or after exercising is really from water loss.

Water is critical for maintaining body tempera- ture and also for removing body wastes and ex- traneous substances. Evaporation of perspiration cools our bodies, and occurs almost constantly. Removal of wastes and extraneous substances occurs through urine (waste products are dis-

Chapter 12. Water–the Body’s Inner Sea ₁₆₁

solved and excreted in urine using relatively large amounts of water) and feces, which contain water. Diarrhea can cause enough water loss to endanger life.

Body water is regulated by the kidneys and our brain’s thirst center. Urine will become concen- trated if water intake is too low, and dilute when we get more than we need. When intake is too low, we become dehydrated, which can lead to heat exhaustion and eventually heat stroke, as the body loses its ability to regulate temperature. This can be fatal, and emphasizes the importance of drinking enough liquids, particularly in hot weather and during heavy exercise.

Because many variables can alter water balance, there’s no specific daily requirement for water. But in general, about a quart of water is needed for each 1,000 calories consumed. In

addition, to drinks, the water in “solid” foods counts, as does the water produced when energy- providing nutrients are metabolized.

Athletes can have special water needs, espe- cially in hot weather, and thirst isn’t a reliable gauge of need. Any advantage conferred by “sports drinks” will generally be due to their car- bohydrate content, and will be limited to endur- ance events lasting more than 90 minutes. While drinking enough water is important, it’s also im- portant to not drink too much.

Much of the water we consume is in food, which is roughly 50% water. Even solid-appearing foods have a lot of water, as their fibrous structures hide the liquid inside. Because water represents so much of food, it must be considered when measuring calorie content or food value.

Most of our drinking water is safe. Hazardous contaminants tend to be localized, as in water from wells in certain areas.

Fluoride in water helps protect against tooth decay, whereas minerals such as calcium and magnesium make the water “hard.” Bottled water, in general, is processed tap water, or spring water, and some may have added carbonation and relatively high levels of sodium. Tap water and bottled water must meet the same Environmental Protection Agency standards.

Figure 12-5: Functions of Water

WATER Cooling Chemical reactions Waste removal Acid balance Resistance to temperature change

Guest Lecturer: Robert S. Swenson, MD

Notes of a Nephrologist