Rehydration salts are one of the cheapest, most quietly important things in a well-built kit — a foil sachet of glucose and mineral salts that, dissolved in water, replaces what your body loses through diarrhoea, vomiting, heavy sweating or a serious bout of the sort of illness that leaves you flat. When you are that dehydrated, plain water alone is not enough: you need the salts and a little sugar to help your gut absorb the fluid and to top up the electrolytes you have been losing. This guide explains what rehydration salts actually do, the difference between medical oral rehydration salts and sport electrolyte tablets, when to reach for them, and why a few sachets belong in every first aid kit, grab bag and car.
They are a natural partner to the water side of a kit. Keep a few sachets with your first aid kit and alongside your stored water, carriers and bottles, so that the means to rehydrate and the means to make water safe live together. For the wider picture on staying hydrated in hot weather see our heatwave preparedness guide, and for storing the water itself, our guide to storing water for emergencies.
What rehydration salts actually do
Oral rehydration salts (ORS) are a precisely balanced mix of glucose (sugar) and electrolytes — mainly sodium and potassium — designed to be dissolved in water and drunk. The clever part is the glucose: sodium and glucose are absorbed together in the gut, so the sugar effectively pulls the salt and water across the gut wall far more efficiently than water alone. This is why ORS is the World Health Organization's standard treatment for the dehydration caused by diarrhoea, and why it works when you are too unwell to keep much down: small, frequent sips replace fluid and salts faster and more gently than gulping plain water, which can pass straight through.
That is the whole point of keeping them in a kit. Dehydration is what actually makes a stomach bug or a hot day dangerous, especially for children, older people and anyone already unwell — and it is easily missed until someone is dizzy, headachey and flagging. A sachet weighs nothing, stores for years, and turns a glass of water into something that genuinely helps. It is one of the highest-value, lowest-cost items you can add to a first aid kit.
Oral rehydration salts vs sport electrolyte tablets
The two products people confuse do related but different jobs. Medical oral rehydration salts — the Dioralyte-style sachets in our picks — are formulated to treat dehydration from illness: the sodium and glucose balance follows medical guidelines, and they are what you want when someone has diarrhoea and vomiting, or is genuinely dehydrated and unwell. They are deliberately not very sweet or 'sporty'; they are a treatment, not a drink.
Sport electrolyte tablets — the Styrkr-style hydration tablets in our picks — are designed to replace salts lost through heavy sweating during exercise or in the heat, and to make water more pleasant to drink so you actually keep drinking it. They typically have less sugar and a more balanced salt profile aimed at performance and heat, and they taste good, which matters on a hot walk or a long day of work. For an emergency kit the honest split is simple: keep medical ORS for illness and serious dehydration, and keep electrolyte tablets for heat, heavy exertion and encouraging fluid intake. Both are useful; they are not interchangeable, and for treating a sick child or a vomiting adult you want the medical ORS.
When you actually need them
The clearest use is diarrhoea and vomiting — a stomach bug, food poisoning, or a norovirus outbreak that sweeps a household in winter. This is exactly when the mains might still be on but you are too unwell to shop or cook, and it is when dehydration does the real harm. ORS lets you replace fluid and salts in small sips even when you cannot face food, and it is especially important for children and older relatives, who dehydrate faster and hide it better. A few sachets in the first aid kit turn a miserable 48 hours into something you can manage at home.
The second use is heat and heavy sweating: a heatwave, a hot day of physical work, or a long walk in summer, where you lose salt as well as water and plain water alone can leave you feeling worse. Electrolyte tablets are ideal here. The third is any situation where clean water is short and every drink needs to count — a water outage, a long journey, or recovery after strenuous effort. In all cases the salts do nothing to make dirty water safe, so pair them with your means of treating water — boiling, a filter or purification tablets — and dissolve the salts only in water you already trust.
How to use them safely
Follow the packet exactly, because the dose is what makes them work and safe. Dissolve each sachet or tablet in the stated volume of water — usually a specific amount for a sachet — and do not make it stronger 'to help', as too much salt is harmful, especially for children. Use clean drinking water (cooled boiled water for infants), not fizzy drinks or juice, which throw off the balance. Sip slowly and often rather than gulping: for someone who is vomiting, a spoonful every few minutes keeps far more down than a glassful at once. Make up a fresh batch as directed and discard any made-up solution after the stated time, typically within 24 hours and kept cool.
A homemade version — roughly six level teaspoons of sugar and half a level teaspoon of salt in a litre of clean water — is the recognised emergency fallback if you have no sachets, but the shop-bought salts are cheap, correctly balanced and far safer to get right under stress, which is exactly why you keep them. Know when to get help: seek medical advice if there is blood in vomit or stools, if a baby, young child or frail older person is affected, if someone cannot keep any fluid down, or if there are signs of severe dehydration such as confusion, sunken eyes, very little or no urine, or drowsiness. Rehydration salts treat mild to moderate dehydration; they do not replace a doctor when someone is seriously unwell.
What to look for when buying
Decide what the kit is for. For treating illness — diarrhoea, vomiting, a sick child — buy medical oral rehydration salts such as Dioralyte, which follow the recognised ORS formulation and are what a pharmacist would recommend. For heat, sport and everyday hydration, buy electrolyte hydration tablets, which taste better and encourage you to keep drinking. Many kits sensibly carry both. Check the sachet or tablet count so you know how many doses you have — a household bout of D&V gets through them faster than you expect — and check the shelf life, which is usually a few years, so you can stock and rotate.
Prefer individually foil-wrapped sachets or blistered tablets for storage: they stay dry and last for years, which suits a stock-once kit, whereas a loose tub degrades faster once opened. Sugar-free electrolyte tablets suit anyone watching sugar for daily use, but for treating illness stick to standard medical ORS, which needs the glucose to work. Our rehydration salts picks cover both archetypes — medical ORS sachets for illness and dehydration, and electrolyte tablets for heat and exertion — so you can carry the right one for each job.
How they fit a UK kit
Rehydration salts sit at the junction of your first-aid and water planning, and they belong in three places. In the first aid kit at home, they are the answer to the winter stomach bug and the summer overheat — the everyday emergencies far more likely than any dramatic scenario. In the grab bag and the car, a few sachets weigh nothing and cover heat, illness and dehydration on the move. And alongside your stored water and carriers, they make sure that if fluid is short, what you do drink works as hard as possible.
Stock a handful of medical ORS sachets and a tube of electrolyte tablets, note the expiry, and rotate them into normal use occasionally so they never sit past their date. Pair them with the means to make water safe — a filter or purification tablets — and with energy bars for when appetite returns, and you have covered the unglamorous but genuinely common emergency: someone in the house who is dehydrated and unwell. For the surrounding plans, see our heatwave preparedness, first aid essentials and winter first aid kit guides.
The short version
Rehydration salts replace the fluid and electrolytes lost to diarrhoea, vomiting and heavy sweating, and they work when plain water alone does not because the glucose helps your gut absorb the salt and water. Keep medical oral rehydration salts (Dioralyte-style) for illness and serious dehydration, and electrolyte tablets for heat and exertion — both are useful and not interchangeable. Follow the packet dose exactly, sip little and often, dissolve only in water you trust, and know when to seek medical help. A few sachets in the first aid kit, grab bag and car are among the cheapest, highest-value additions you can make. See our rehydration salts picks and our heatwave preparedness guide.
