Water and food for a longer ruck

There is no honest universal litres-per-hour rule. Sweat rate changes with body size, pace, load, temperature, humidity, clothing and acclimatisation. Start normally hydrated, carry enough for the route and conditions, drink according to thirst and a plan you have tested, and avoid both large fluid deficits and forced overdrinking.

Water is also load: one litre is almost exactly one kilogram. That is useful, because it makes the pack progressively lighter, but it means the morning pack weight and finish pack weight are not the same. Count the water when weighing the start load.

Match the plan to the session

Estimate your sweat rate

For a representative training hour, weigh yourself in minimal dry clothing before and after. Add the fluid you drank and subtract urine produced; the change is an estimate of sweat loss. One kilogram of mass change is approximately one litre of water. Divide by the session hours to estimate litres per hour for those conditions.

The result is not a command to replace every drop while moving. Formal guidance aims to avoid excessive dehydration while also avoiding weight gain from overdrinking. Repeat the test in different weather and use the range to decide what to carry and where to refill.

When electrolytes matter

Sodium in drinks can improve palatability and fluid retention during long, sweaty exercise. It matters more in heat, for salty sweaters and over multiple hours. It is not required in every bottle for a cool forty-minute walk, and it does not make an inadequate water supply adequate.

Use a product at its labelled concentration and test it in training. Making a drink much stronger than intended can upset the stomach; making it extremely weak while drinking huge volumes does not solve overconsumption.

Fuel the work you are actually doing

A normal meal is enough for most short rucks. Once a session becomes a sustained endurance effort, small regular carbohydrate portions can preserve pace and decision-making. Sports-nutrition position statements commonly discuss 30–60 g of carbohydrate per hour for prolonged hard exercise; that is a range to practise toward when the effort requires it, not a mandatory ration for every easy walk.

• Choose food you can chew while breathing and walking: banana, soft bar, sandwich pieces, dried fruit or a familiar drink mix.
• Start before hunger becomes urgent on sessions lasting several hours.
• Use event day to repeat known choices, not to test a new gel or concentration.
• For multi-day marches, ordinary meals and total daily intake matter more than any single trail snack.

Build the carry plan

Write down duration, expected conditions, refill points and what happened in a similar training session. Then carry a small margin. Remote heat needs more margin than an urban route passing fountains and shops. The packer should reflect consumables at the start, even though the centre of gravity and total weight change as you use them.