Taper week hydration is about topping off, not loading up. In the seven days before a marathon your training volume drops by roughly half, your sweat losses drop with it, and the job shifts from replacing fluid to simply arriving at the start line normally hydrated with full glycogen stores. The runners who show up flat on race morning are usually the ones who drank plain water all week, diluted the sodium their body was trying to bank, and mistook frequent bathroom trips for good hydration.
What Actually Changes During Taper Week
Fluid needs scale with sweat rate, and sweat rate scales with training load. When a 16-mile long run becomes a 6-mile shakeout, you may be losing a liter or two less fluid per session than you were three weeks ago. Keep drinking at peak-week volume and the surplus does not get stored as useful hydration. It gets urinated out, and it takes sodium with it.
The target for taper week is euhydration, not superhydration. There is no meaningful way to pre-load water the way you can pre-load carbohydrate. Your kidneys will defend plasma volume by dumping whatever you drink beyond need, typically within an hour or two. Pale straw urine, stable morning body weight, and the absence of thirst are the three markers worth tracking. If your urine is completely clear all week, you are almost certainly overdrinking.
Carb Loading Is Quietly a Water Load Too
Every gram of glycogen your muscles store is bound with roughly three grams of water. That is why carb loading and hydration are the same conversation. Current guidance for trained endurance athletes is 8 to 12 grams of carbohydrate per kilogram of body weight per day for one to three days before the race. The old seven-day depletion-then-load protocol is obsolete for most modern runners.
Expect the scale to move. Full glycogen loading typically adds 2 to 4 pounds, or about 2 to 3 percent of body weight, almost entirely as stored fuel and the water attached to it. That is a sign the protocol worked, not a sign you got sloppy. Most runners return to baseline weight within 24 to 48 hours after the race.
The practical error is under-drinking during the carb load. Water is required to store glycogen, so if you eat 10 grams per kilogram of carbohydrate on a restricted fluid intake, you cap the very thing you are trying to maximize. Pair every carb-heavy meal with a glass of fluid, and make at least a couple of those glasses contain sodium.
The Sodium Question: How Much, and What Sodium Cannot Do
Sodium is what lets you hold on to the fluid you drink. It raises plasma osmolality slightly, which stimulates thirst and reduces urine output, so a sodium-containing drink keeps more of itself in circulation than plain water does. The American College of Sports Medicine points to roughly 500 to 700 mg of sodium per liter of fluid for replacement purposes, and 300 to 600 mg of sodium per hour during exercise lasting more than two hours.
Those numbers are a useful anchor for taper week too. If you are drinking three liters a day and all of it is plain water, you are diluting rather than topping off. Getting a portion of your daily fluid from an electrolyte source, plus salting food normally, is a more effective way to arrive hydrated than volume alone.
One important caveat, because it gets oversold every marathon season: sodium supplementation has not been shown to reliably prevent exercise-associated hyponatremia. The evidence is genuinely insufficient. The dominant risk factor for hyponatremia is fluid overload, not sodium depletion. Drinking to a schedule that roughly matches your sweat rate, rather than drinking as much as possible, is the actual protective behavior.
Where to get taper-week sodium
- High-sodium electrolyte drinks. LMNT sits at about 1,000 mg of sodium per stick, and Skratch Labs Hyper Hydration is formulated in a similar range for pre-race and hot-weather use. These are deliberate tools, not all-day beverages.
- Moderate everyday options. Gatorade Endurance and Nuun Sport land in a lower sodium band that suits taper-week shakeout runs, when sweat losses are small.
- Food-first sodium. Broth, salted rice, pretzels, olives, and normal seasoning at meals will carry a surprising amount of the load without any powder at all.
- Pickle brine. Ounce for ounce, pickle juice is among the most sodium-dense things in a runner kitchen. Products like Fast Pickle package it in single-serve shots, which is easier to dose than free-pouring from a jar. Worth noting that the research on pickle juice and muscle cramps points to a rapid oropharyngeal reflex rather than to electrolyte replacement, so treat it as a concentrated sodium source and a cramp tool, not as a substitute for a full drink mix.
A Day-by-Day Taper Week Hydration Plan
The plan below assumes a Sunday morning race, which covers most of the fall calendar from Berlin through Chicago and New York. Shift the days if your race sits elsewhere in the week.
Monday to Wednesday. Baseline. Roughly 30 to 35 ml of fluid per kilogram of body weight per day, adjusted by thirst and urine color. One electrolyte serving on any day you run. Nothing special, nothing forced.
Thursday. Start nudging carbohydrate upward and salt your meals a little more deliberately. This is the last useful day to test the exact drink mix you plan to use on race morning.
Friday and Saturday. The real carb load, 8 to 12 g/kg per day. Add a second and third electrolyte serving to match the higher carbohydrate intake, since glycogen storage is pulling water into muscle. Drink steadily across the day rather than in large boluses. Stop heavy fluid intake about two hours before bed on Saturday so you are not up at 2 a.m.
Race morning. Roughly 5 to 7 ml per kilogram of body weight two to three hours before the gun, then another 3 to 5 ml/kg 60 to 90 minutes out only if your urine is still dark. A sodium-containing drink beats plain water here, both because it is retained better and because it will not send you into the portable toilet line at minute 40.
What to Skip in the Final 72 Hours
- New products. Race week is the worst possible time to try an unfamiliar powder, gel, or high-dose sodium shot. Everything you use on Sunday should have appeared in a long run already.
- High-fiber carbohydrate. Whole grains and large salads are excellent food and poor carb-loading vehicles. Go with white rice, pasta, potatoes, bagels, and sports drinks.
- Alcohol. It is a diuretic and it degrades sleep quality during the two nights that matter most.
- A sudden caffeine increase. If you plan to use caffeine on race day, keep your normal intake through the week rather than abstaining and then spiking.
- Drinking a gallon “to be safe.” Overdrinking in the final 24 hours is the single most common way recreational runners create a problem that did not exist.
Done right, taper week hydration should feel boring. You eat more carbohydrate than usual, you salt your food, you drink when you are thirsty and a little beyond, and the scale creeps up a couple of pounds. That is the whole protocol. The complexity belongs in the race-day plan, not the week before it.
Frequently Asked Questions
How much water should I drink during marathon taper week?
Roughly 30 to 35 ml per kilogram of body weight per day as a starting point, adjusted for thirst, weather, and how much running you are still doing. For a 70 kg runner that is about 2.1 to 2.5 liters daily from all sources. Increase modestly on the two carb-loading days, since glycogen storage pulls water into muscle. Use pale straw urine as your check, not a fixed number on a bottle.
Should I take electrolytes every day of taper week?
On days you run, yes, at least one serving. On complete rest days, normal salting of food is usually enough. The exception is the 48 hours of carb loading, when two to three electrolyte servings help you retain the extra fluid that glycogen storage requires. Sodium in the 500 to 700 mg per liter range is the useful anchor.
Why did I gain weight during taper week?
Almost certainly glycogen and its bound water. Each gram of stored glycogen holds about three grams of water, so a full load adds 2 to 4 pounds, or 2 to 3 percent of body weight. This is stored fuel and hydration you will spend during the race, and it typically resolves within 24 to 48 hours afterward.
Does pickle juice help before a marathon?
It is a very sodium-dense way to add electrolytes in the days before a race, and a small pre-race dose is well tolerated by many runners. The research on pickle juice and cramping points to a rapid nerve reflex triggered in the mouth and throat rather than to electrolyte replacement, so it is best understood as a concentrated sodium source and an in-race cramp tool rather than a full hydration drink.
Can I drink too much water before a marathon?
Yes, and it is the more common failure mode. Exercise-associated hyponatremia is driven primarily by fluid overload rather than by sodium loss, and sodium supplementation has not been shown to reliably prevent it. Drink to a schedule that approximates your sweat rate instead of drinking as much as you can hold, and be suspicious of urine that runs completely clear all week.
What should I drink on race morning?
A sodium-containing drink beats plain water. Aim for about 5 to 7 ml per kilogram of body weight two to three hours before the start, with a top-up of 3 to 5 ml/kg 60 to 90 minutes out if needed. Use the exact product you have already trained with, whether that is a sports drink, an electrolyte mix, or diluted juice with a pinch of salt.