How Much Should You Drink? A Trail Runner's Hydration Checklist
Trail Notes | Fuelling & Hydration
How Much Should You Drink?
a trail runner's hydration checklist.
You are about to head out the door and you just want the short answer: how much should you actually drink? Here it is, plus the handful of things worth knowing before you fill your bottle.
Sweat rates vary enormously between runners, and generic advice like "drink one bottle per hour" can miss the mark badly in either direction. This is a working checklist, not a rigid number. If you want to find your actual personal number, our sweat-rate testing guide walks you through it.
Your starting point
Your needs shift with your body, your pace, the weather and the day. A cold start and a hot afternoon are not the same. Start with a moderate baseline and adjust from there based on how you feel, not a fixed number you copy from someone else's bottle.
Adjust upward when
It is hot, humid, or you are exposed to direct sun for long stretches.
You are climbing hard and sweating more than usual.
Your clothes are soaked through or your bottles are emptying faster than planned.
Sodium matters
Sodium concentration in sweat varies hugely between runners. It helps maintain fluid balance, nerve function and muscle contraction, and under-replacing it makes cramping, nausea and poor fluid absorption more likely. Some runners need one electrolyte tablet in a bottle, others need two or three. The point is to find your own number, not someone else's recipe.
Signs you may be a salty sweater: white salt marks on your kit, gritty skin, stinging sweat in your eyes, or a strong salt craving after long runs.
Do not just drink more plain water
When a run feels hot or hard, it is tempting to keep drinking more plain water. But drinking large amounts of plain water without enough sodium can dilute your blood sodium and leave you feeling worse, not better. The answer is not simply more water. It is fluid plus electrolytes, matched to conditions.
Stop and reassess if you notice
Confusion, a severe headache, or worsening nausea.
Swollen hands or feet despite ongoing drinking.
Dizziness or feeling progressively worse despite drinking more.
Separate fluid from fuel
You do not have to drink your calories. Take energy from gels, bars or food, then adjust fluid separately based on sweat, thirst and temperature. This gives you far more control across a long day — if it gets hotter, you can increase fluid without accidentally overshooting on carbohydrate too.
The checklist
Before: check the forecast and terrain, fill bottles with your usual sodium mix, pack a backup electrolyte if it is hot.
During: sip regularly rather than gulping, adjust upward for heat or climbing, keep fuel and fluid as separate decisions.
After: note how you felt — thirsty, bloated, clear-headed, crampy — and adjust the plan for next time.
Her Trails coaching cue
Your gut is trainable. Use long runs to rehearse how much fluid and sodium you can tolerate, in heat and cold, on climbs and descents. Mistakes in training are useful. Mistakes on race day are much harder to fix.
Want your actual number?
This checklist gives you a working starting point. For a step-by-step sweat-rate test, plus how hydration needs shift across your menstrual cycle and through perimenopause, see How to Test Your Sweat Rate (and Why Hydration Changes Across Your Cycle).
Written by the Her Trails coaching team
Trail Notes are evidence-informed coaching journals written for women who train, race and run on trails.
