A glass of tap water and a plastic bottled water: There’s no difference in the hydration level; just taste and status appeal. (Bill O'Leary/The Washington Post)

It’s sweltering outside and you’ve worked up a big thirst, so you duck into a grocery store to pick up a bottle of water. But these days there are so many brands and types on the shelves that you could drop from dehydration before figuring out which one to buy.

Regardless of their prices or promises, all the waters on the market hydrate you equally well, and no better than tap water does. So if that is all you care about, just grab the cheapest. Even better, remember to fill up a bottle at home before you leave next time. But if you want something that tastes different or has the possibility of added health benefits, here’s the lowdown on what’s out there.

Water, plain and simple

Bottled water, as defined by the Food and Drug Administration, which regulates the industry, is simply water fit for human consumption that is bottled safely. It could be packaged tap water. But beyond that baseline there are official definitions for terms such as “purified,” “spring,” “artesian” and “mineral” that specify how the water is processed and sourced.

“Purified” means the water — from any viable source, even, say, a municipal water supply — has been filtered or distilled to remove impurities such as chlorine and other elements that affect taste. Spring and artesian waters come from specific sources: spring water from an underground formation that flows naturally to the surface, and artesian water, which is tapped from an underground aquifer that’s under pressure. Although spring and artesian are often more expensive and have chic packaging, they do not offer any benefits beyond, perhaps, a special taste and status appeal.

Mineral water is defined as having 250 parts per million dissolved solids naturally present (no minerals may be added) and must originate from a protected underground source. Most of these waters are so mineral-rich that drinking them can significantly boost your intake of the nutrients, especially calcium and magnesium, which many people lack. Plus, mineral water tends to be alkaline, which may help bone health. (More on that later.) Depending on the brand, one liter a day can cover you for 20 to 58 percent of calcium and 16 to 41 percent of magnesium needs. On the flip side, it can also contribute a significant amount of sodium, so read the label carefully to decide what is right for you.

Flavored waters

For those who don’t care for the taste of plain water, there is a vast array of flavored options. Some are simply treated with a hint of natural fruit and/or herbal essences. Others have sweeteners, food colorings and artificial flavors, making them, to me, more like soft drinks than water. Many sweetened waters contain considerable calories from refined sugar, upwards of 50 calories per cup (120 in a typical 20-ounce bottle), which can really add up if you are chugging several each day. Many also have promising names like “Revitalize” or “Focus,” which are mainly marketing tools that are better ignored, and vitamin and herb enhancements that probably won’t hurt you but won’t benefit you much, either. When picking up flavored water, I suggest going for one that is as much like actual water as possible, unsweetened and with minimal additives.

Plant-derived waters

When coconut water first burst onto the scene, it promised better hydration than water, but marketers have since backed off on that unjustified claim. What it can claim to be is a lightly sweet liquid with a somewhat nutty taste that hydrates as well as water and provides a significant dose of potassium. Coconut water comes from the inside of the young green fruit and, unlike coconut milk, has no fat. If you want a change of pace flavor-wise and you take into account the 45 calories it has per cup (if you get the unsweetened variety), it can be a good way to change things up. But there is nothing magical about it. You could also hydrate and replenish your potassium (plus get other nutrients and filling fiber) by drinking a cup of water and eating a small banana.

A new kid on the shelf in the same category is maple water, the liquid (sap) from the maple tree that is usually boiled down to make a syrup. In its unconcentrated form, it is clear and has a subtle sweetness, plus some minerals, for about 20 calories per cup. There isn’t enough research to back the many claims about its health benefits, including the “cleansing” power I was told it has by the woman providing tastes of it at my local market. (I hope she didn’t see me rolling my eyes.) But I thought it was delicious, if expensive, at $4 for a small bottle, and, like coconut water, a healthy way to switch things up taste-wise.

pH alkaline waters

An overwhelming trend in the beverage aisle is the emergence of “pH-balanced” alkaline waters — boasting a pH greater than 7. The trend stems from a popular but unfounded theory that if we consume too much water that is on the acidic side (which tap water often is), we wind up acidifying our body and compromising our health in myriad ways. The fact is, our body’s pH is maintained in a tight range, thanks to our kidneys and other buffering systems, and there is no substantial research to show that drinking more acidic water does any harm per se. But while there is no need to stress about your water’s pH, there is one well-documented “pro” to drinking water that is more alkaline: It could benefit your bones.

Several studies show that drinking water that is more alkaline because of its electrolyte and mineral content (whether naturally occurring, as with mineral water, or added) can help preserve bone by reducing the kidney’s need to tap into calcium reserves to balance normal acid in the body. So, not only do you ingest more important minerals and nutrients like potassium when you drink this kind of water, you also help keep calcium in your bones instead of breaking it down. Skip brands that have been made alkaline through a process of ionization, which won’t give you the nutrient benefit that minerals and electrolytes do. Also keep in mind that more alkaline (a higher pH) is not necessarily better. Aim for a pH somewhere between 7.5 and 8.5, because once you get above that, the water tends to have a slippery feel and less appealing taste. With all the options out there, you shouldn’t settle for less than one that delivers both good health and good taste.

Krieger is a registered dietitian, nutritionist and author. She blogs and offers a biweekly newsletter at www.elliekrieger.com . She also writes weekly Nourish recipes in The Washington Post’s Food section.

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