Dr. Gerald Pollack at the University of Washington calculated that 99% of the body’s molecules, counted individually, are water molecules. Whether you use that number or the more commonly cited 60-70% by volume, the point is the same: water is not a background player in your body. It is the main event.
Now here is the question that should follow from these numbers, and almost never does:
Are those water molecules actually where they need to be?
That is the question hydration science should have been asking all along. Instead, we spent decades asking a much simpler but far less useful question: how many ounces did you drink today?
The Ounce Obsession Cost Us
Eight glasses a day. Half your body weight in ounces. Drink until your urine is clear. These guidelines became so embedded that most people treat them as established science. They are not. There is no strong clinical evidence that this intake translates to optimal hydration and the resulting physiological benefits in your body.
And by focusing entirely on intake, on the ounces going in, we missed the thing that actually determines whether you're hydrated: what your body does with the water once it arrives.
Most people are drinking enough water. Most people are not optimally hydrated.
Those two sentences can both be true at the same time. Understanding why is everything.
What Hydration Actually Is
Hydration is not a measure of water intake. Hydration is water present in sufficient quantity in all of the places your body needs it — your cells, your blood, your lymphatic system, your gut lining, your joints, your brain.
Your actual hydration needs depend on your size, your activity level, your stress load, your environment, your medications, the quality of the water you're drinking, how well your digestive system is functioning, and a dozen other variables that a single daily ounce target cannot capture.
Drinking water gets water into the start of your digestive tract — your mouth. That is step one. But water moving from your digestive tract into your cells, tissues, and organs is a completely separate biological process. And it requires more than just water. It requires minerals. It requires a gut that can absorb. It requires optimal not elevated blood sugar. It requires a stress response that isn't chronically overactivated.
When all of those conditions are met, your body behaves like a sponge — absorbing water and distributing it to where it needs to go.
When they aren't, your body behaves like a hose — water runs through, comes back out, and does very little along the way.
Hose vs. Sponge — Which One Are You?
The hose is more common than most people realize. Signs you may be running in hose mode:
• You drink water and need to urinate within a short time
• You feel tired even when you're sleeping enough
• Your skin is dry or dull despite drinking plenty of water
• You're constipated, or your stools are dry and pellet-like
• You get headaches, muscle aches or have joint pain
• You feel hungry shortly after eating
• You have high blood pressure or high blood sugar
• You're struggling to lose fat despite consistent effort
That last one stops people. Fat loss and hydration don't get discussed together often enough. But they are deeply connected — and I'll come back to that in a moment.
The sponge state is what we're working toward. When you're a sponge, water reaches the places that need it. You're not running to the bathroom constantly. You're not perpetually thirsty. Your energy is stable. Your digestion works. Your body has what it needs to do its job.
What Your Urine Color Does — And Doesn't — Tell You
Before I go further, I want to correct something you've probably been told — including possibly by your doctor.
Urine color can tell you if you ARE dehydrated. Dark yellow or amber is a reliable signal that you need water now. And to investigate what’s contributing.That's accurate and useful.
But pale yellow or clear urine does not tell you that you ARE hydrated. Especially not optimally hydrated. It tells you that you are not currently dehydrated. Those are two completely different things.
Your body can be running water straight through, in “hose” mode, absorbing almost nothing and your urine can still look completely normal. This is why so many people who track their ounces, check their urine, and feel like they're doing everything right still experience every symptom on the hose list above.
There is a simple at-home experiment my colleague shared with me that I use with all my patients. It’s easy and doesn’t require purchasing any test kit etc. It tells you within two hours whether your body is truly absorbing water or running it straight through. It takes nothing more than a glass of water and a timer. It’s the “Hose or Sponge” experiment. I'm not sharing it here because the result alone isn't enough. You need how to interpret your results and that’s more than I have room to write here. The full protocol, including exactly how to interpret and address your result, is in my book Your Best Shot.
Why This Is a Weight Health Problem — Not Just a Wellness One
Here is what the ounce obsession caused us to miss: hydration is not a hydration issue. It is a weight health issue. And the mechanism runs deeper than most people know.
When your body is in hose mode — when water isn't reaching your cells in the quantities they need — several weight health consequences follow simultaneously.
Fat metabolism slows.
Your liver is one of the primary organs responsible for metabolizing fat. It also serves as a backup for the kidneys when the body is inadequately hydrated. When your cells are running dry, your kidneys call on the liver for support — which means the liver has less capacity to do its fat metabolism work. Dehydration at the cellular level is a direct brake on fat burning.
Toxin elimination stalls.
Your body's detoxification pathways — through the liver, kidneys, lymphatic system, and digestive tract — all require water to function. When cellular hydration is insufficient, the body's ability to move waste and toxins out is compromised. Those toxins can be stored in fat tissue as a protective mechanism, making fat loss even harder.
Meet PYY: The Weight-Health Hormone Managing Your Hydration Right Now
Peptide YY aka PYY is a hormone produced in the L-cells of your gut, primarily in the ileum and colon. IF you’ve heard of it you know it as a satiety hormone released after eating proteins and fats. That’s its job is to tell your brain you’ve had enough. That part is true. But it’s the smaller part of the story.
PYY’s other job: it is an active regulator of water and electrolyte absorption in your colon. This is not a passive role. PYY directly controls how much water your colon pulls from stool before that stool is eliminated.
Here’s why that matters for you personally.
When your body senses it needs more water (cells don’t have enough), PYY responds by increasing water absorption from the colon. Your gut is doing what a smart system does: looking for available water and taking it from wherever it can find it. Stool happens to be a source.
The consequence of that protective mechanism is something you’ve probably experienced but never connected to hydration: dry, hard, pellet-like stools. Constipation. Your body didn’t fail to digest properly. It extracted the water from your waste before it could be eliminated, because it needed that water more urgently elsewhere.
This means constipation is not just “a fiber problem” or even “a motility problem”. It is a hydration status signal; your body’s way of telling you that water isn’t reaching the places that need it. And if you’ve been adding more fiber in response, without addressing hydration, you may have uncomfortably noticed it doesn’t fully solve the problem. Fiber without optimal water in the intestines can actually make constipation worse.
PYY’s dual roles — managing both satiety signaling and colonic water absorption — makes it one of the most important weight-health hormones to understand. When your hydration is adequate, PYY can do both jobs well: absorb the right amount of water, signal satiety appropriately, and keep your digestive system moving. When hydration is insufficient, PYY prioritizes water recovery and your stool, elimination, your appetite signaling, and your weight health all pay the price.
What This Hydration Month Is About
Over the next four weeks, I am going to walk you through the complete picture:
• Why water needs a team of electrolytes, in optimal amounts and usable forms. How to measure and choose the right ones for your body
• The hidden dehydrators; which of your choices could be working against you every day (some will surprise you)
• How water quality — not just quantity — impacts how your body uses what you consume.
• Practical, genuinely enjoyable ways to upgrade your hydration without obsessing over ounces
We are also going to talk about creatine, PYY in more depth, coconut water ice cubes, and why your morning coffee has probably been miscounted for years.
But start today with one shift: stop asking how many ounces you drank, and start asking whether your body is actually absorbing and using the water you're giving it. That question — hose or sponge — is where the real work begins.
— Ashley Koff, RD
The “backwards DR”
Want to know if your body is truly hydrated — not just not dehydrated? Get the experiment and how to assess your results in Your Best Shot.
Or if you'd rather figure it out together: book a free 15-minute personalized nutrition session at The Better Nutrition Program. We'll look at your specific picture and figure out where to start.
Subscribe to follow along all June. If you have the means upgrade to support my work. Every week is a new piece of the hydration puzzle — and by the end of the month, you'll have a complete strategy built around your body, not a formula.
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