Why Kids Arrive at Practice
Already Dehydrated
You blow the whistle. Practice starts. And most of your athletes are already behind — not because they didn't warm up, but because they walked onto the field in a state of dehydration they probably don't even know about.
This isn't a new problem, but it's a poorly understood one. Research from the University of Arkansas found that up to 75 percent of young athletes between the ages of 8 and 18 are dehydrated before they even arrive at practice.1 Another study found that almost two-thirds of children showed signs of dehydration before a single drill was run — and 25 to 30 percent showed signs of serious dehydration.2
Think about that for a second. Before your practice even begins, you may be coaching a group of kids who are already operating at a deficit. And by the time any of them feels thirsty enough to say something, the gap has only gotten wider.
So how does this happen? And what can you actually do about it?
The School Day Does More Damage Than Most Coaches Realize
A kid who has been in class all day, eaten lunch in a noisy cafeteria with 10 minutes to spare, and then sat on a bus to get to practice has been fighting dehydration since they woke up — and losing.
Research published in Harvard's Nutrition Journal found that nearly half of all school-age children in the U.S. are inadequately hydrated, with about 25 percent not drinking water at any point during the day.3 A 2025 systematic review of hydration studies across children and adolescents found that 81 percent of studies among young athletes reported dehydration — and 69 percent found dehydration among non-athlete kids too.4 This is not a sports problem. It's a baseline problem that sports makes worse.
The reasons aren't hard to understand once you look at a typical school day. Water fountains that are old or taste bad. Cafeteria lines too long to grab a drink before the bell rings. Class schedules with no real hydration breaks. Schools where bringing a water bottle isn't encouraged or even permitted. Research published in Frontiers in Public Health identified these access and environmental barriers as significant contributors to inadequate hydration in school-age children, with water availability proving to be a stronger predictor of consumption than any amount of encouragement or education alone.5
Add to that the simple reality that kids choose beverages that taste good. Sugary drinks, sports drinks, juice — all common in cafeterias and vending machines — create the illusion of hydration while often working against it.
By 3 p.m., when practice starts, the school day has already done its damage.
They Woke Up Behind
Here's something most people don't think about: the human body loses fluid during sleep. Breathing alone expels water vapor all night. Add a warm room, a heavy blanket, or a kid who runs warm, and they can wake up meaningfully dehydrated before the day even starts.
Research on adolescent athletes consistently finds that hydration status assessed first thing in the morning — before any exercise — already shows a fluid deficit in a significant portion of young athletes.6 They start breakfast behind. They go to school behind. They come to practice behind.
And the fix — drinking a big glass of water at breakfast and carrying a water bottle through the school day — sounds obvious, but it's simply not how most kids operate. Habits around hydration are built over time with consistent reinforcement, and for most youth athletes, nobody has ever told them that what they drink between 7 a.m. and 3 p.m. matters for what happens at 4 p.m. on the field.
Thirst Is Not a Reliable Warning System in Kids
This is the part that catches most coaches off guard.
We instinctively trust thirst as the signal to drink. But in children, the thirst response lags significantly behind the actual fluid deficit. By the time a young athlete tells you they're thirsty, research suggests their hydration deficit is already two to three times greater than the 1 percent threshold that begins to affect cognitive and physical performance.7
And the effects of that deficit aren't just physical. A study published in Appetite found that even mild dehydration negatively impacted cognitive performance in children ages 6 to 7.8 A separate study of 58 children ages 7 to 9 showed that those who drank additional water performed measurably better on visual attention, letter-cancellation, and memory tasks compared to those who didn't.9 A study of 40 eight-year-olds found that memory recall was significantly better after drinking just 300 ml of water.10
What this means on the field: a kid who looks distracted, slow to react, or just "off" may not be having a bad day. They may simply be running on insufficient fluid. Their brain is not firing the way it should, and they arrived that way before you ever called the first drill.
What Coaches Can Do About It
You can't control what happens during the school day. But you can control what happens before and at the start of practice.
Ask before you assume. Make "did you drink water today?" a standard question at the start of every practice — not accusatory, just a genuine check-in. Most kids will be honest, and it opens a conversation about why it matters.
Set a pre-practice hydration standard. The American Academy of Pediatrics and CHOC Children's Hospital recommend that athletes drink 16 to 20 oz of water two to three hours before practice, and another 8 to 10 oz in the 10 to 20 minutes just before activity begins.11 Share this with your athletes and their parents. Put it in your practice notes. Make it part of the routine.
Use the urine color check. It's not glamorous, but it works. Pale straw color means well hydrated. Dark yellow or amber means they need to drink before starting. This is something athletes can self-monitor, and teaching it once goes a long way.
Consider electrolytes for longer or hotter sessions. When athletes arrive dehydrated and then sweat through a 90-minute practice in summer heat, plain water may not be enough to close the gap. Sodium, potassium, and magnesium help the body actually absorb and retain fluid rather than just passing it through. For sessions over 60 minutes or in warm-to-hot conditions, an electrolyte supplement like Acuity Sport is a practical way to catch athletes up and keep them there.
Loop in the parents. The biggest lever coaches have is what happens at home. A one-page handout or a quick email to parents explaining the pre-practice hydration window — and why it matters — does more than any water break you call during practice. Parents who understand that morning and afternoon hydration directly affects their child's performance will reinforce the habit at home.
The Game Is Won or Lost Before the First Whistle
Your athletes are not starting practice on a level playing field. A significant number of them — potentially most of them on hot days — are already at a deficit that affects how they think, react, and perform. That deficit didn't start when they stepped on the field. It started when they woke up.
The good news is that this is entirely fixable. It just requires treating pre-practice hydration as part of your coaching — not an afterthought, and not the athlete's problem alone to solve.
Water breaks during practice matter. But the game is won or lost in the hours before you blow the first whistle.
Pre-practice hydration is coachable. Ask athletes what they drank today, set a simple pre-practice target, teach the urine-color check, and get parents on board. Small routines before practice outperform reactive water breaks once practice has already started.
- University of Arkansas News — Research: Dehydration Likely Among Young Athletes
- SouthCoast Health — Playing It Safe with Dehydration and Youth Sports
- CBS News / Harvard Study — U.S. Kids Aren't Drinking Enough Water
- PMC / MDPI Children — Children, Adolescents and Urine Hydration Indices — A Systematic Literature Review on Athletes and Non-Athletes (2025)
- Frontiers in Public Health — Stakeholder Perspectives of Barriers and Facilitators to Enhancing Hydration in Elementary Schools (2026)
- PubMed — Hydration in the Pediatric Athlete — How to Guide Your Patients
- American Society for Nutrition — Water Consumption Affects Cognitive Function in Children
- ResearchGate / Journal of Nutrition — Cognitive Performance and Dehydration
- ScienceDirect — Hydration, Mood, and Cognition in Primary School Aged Children in the United Kingdom
- PublicSchoolWORKS — How Does Student Hydration Affect Academic Performance?
- CHOC Children's Hospital — How to Make Sure Your Young Athlete Stays Hydrated During Sports
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