Today, class, we are going to discuss water bottles and how they seem to be everywhere; hanging off yoga mats or gym clothes of everyone from world leaders to your neighbor working out on the stationary bike next to you. Kids as young as kindergartners trek to school every morning hunched over by the weight of their backpacks, trudging to school to the rhythm of their water bottles banging against their pack.

What is our fetish with water bottles? If we were a culture of nomads, in a desert with few if any sources of water, then it makes perfect sense to carry your water with you. But from the locker room to the fitness center or gym, there are at least two water fountains. And lest I keep myself awake all night worrying about drought, our average rainfall each year is about 47 inches, plus 60-something inches of snow, so I’m sorry, but I don’t see the water bottle as a necessity to our lives.

My exercise class takes place in a room with a water fountain right outside the door. Yet when the instructor says get some water, most people take their water bottles out.

Early adventurers brought their water or wine in goatskin that they carried across a shoulder. Such goatskins were made from the stomach or bladder of a cow or goat or lamb. I know this because I saw a lot of movies with goatskins used in such a way. It seemed like every Greek partisan in movies like “The Sun Also Rises” and “Zorba the Greek,” not to mention the iconic Errol Flynn version of Robin Hood, had a goatskin that they would hold up in front of them, aim and squeeze a mouthful of vino into their mouths. We came out of those dark matinees full of images of heroic peasants armed with scythes and goatskins fortified with wine they had pressed themselves.

Plastic changed all that. The water bottles you see now, attached to someone’s rolled up yoga mat, usually have a logo or some sponsor who paid for the opportunity to provide you a way to carry water. The bottles themselves seem to have a basic delivery system, from your standard screw cap to a pop-up nipple. Compared to a goatskin, which can propel a few drops of water from a foot or two away, the screw cap is absolutely boring. Can you imagine Errol Flynn as Robin Hood unscrewing a plastic water bottle and drinking from it like an ordinary person? The latest iteration is from a brand called Camelbak, where the water rests in some kind of container you wear on your back like a backpack. The water arrives in your mouth via a clear plastic tube.

According to groups that keep track of such things, the average household in the U.S. uses 138 gallons of water per day. Apparently, there is no such thing as drinking too much water, or at least over indulgence doesn’t seem to occur very often. But it does occur.

When we drink too much water too fast we can fall into a state of water intoxication, or hyponatremia, which can be fatal. The thing with hyponatremia is that it won’t happen if you’re exercising or involved in strenuous activity — strenuous activity like changing channels on the television or opening another bag of Doritos doesn’t count.

Water bottles, like t-shirts during the running fad in the 1980s, have become an advertising medium. Every organized race gets you a T-shirt advertising the race or the sponsor or both. I’d love to continue this conversation, but I’m thirsty.

Bob Kalish is a Coastal Journal contributing writer. He can be reached at [email protected].