How much water does a horse drink a day? (And why winter is the risky season)

A 500 kg horse in light work typically drinks 21 to 29 litres of water a day on a mixed diet or grass, close to double that on dry hay alone, and 60 to 70 litres for a mare in milk.

The catch is that the amount changes with the season, and in autumn it runs the wrong way: more hay, colder water, less drinking.

This post covers the numbers in litres, why winter is when intake quietly drops, what the research says about warm water, how to tell whether your horse is drinking enough, and when to ring the vet.

How much water does a horse drink a day?

The clearest figures are in the MSD Veterinary Manual’s chapter on horse nutrition, last reviewed in February 2026. Here is what it gives, worked out for a 500 kg horse:

The arithmetic for the first and last rows: 500 kg is five lots of 100 kg, so 5 × 5 = 25 litres, and 5 × 12 to 5 × 14 = 60 to 70 litres. Scale it for your own horse. A 350 kg pony at the 5 L per 100 kg minimum is 3.5 × 5 = 17.5 litres.

In buckets, which is how most of us actually think about it: a 15 litre bucket holds a little over half of a 25 litre day. So a stabled horse in light work on a mixed diet needs to be draining somewhere between roughly one and a half and two buckets a day, and a horse on hay alone noticeably more. Your buckets may not be 15 litres, so fill one from a jug once and find out.

Treat these as ranges, not targets. What matters most is what is normal for your horse, and whether that changes.

Why does a horse on hay drink more than a horse on grass?

Because grass is wet and hay is not. A horse at grass takes in a good part of its water with its food, and may barely visit the trough on a mild day. Hay is dried forage, so a horse living on it has to drink nearly all its water. The MSD manual puts it simply: horses fed only dry hay can almost double their water intake.

This is the hinge of the winter problem. Autumn is when grass dies back and horses move onto haynets. Our post on how much hay a horse needs covers the forage side, and every extra kilo of hay is dry food that needs water with it.

Why do horses drink less in winter?

Partly because the water is cold, and partly because it is sometimes not there at all. The British Horse Society’s colic guidance notes that horses may drink less in colder weather and when water sources are frozen, and also when water is dirty, the supply runs short or another horse guards it.

Put that next to the hay point and you have the risk. The horse needs to drink more from a bucket or trough at exactly the time it is inclined to drink less.

The worry is impaction colic, where the gut becomes blocked and food stops moving through. The MSD manual says inadequate water access increases its incidence. A 2019 systematic review of colic risk factors, from the University of Nottingham, found three studies looking at water, two of which reported a higher risk of colic with no or reduced access to water. The evidence is about access and intake, not winter on its own, but winter is when access and intake are most likely to slip.

Does warm water make horses drink more?

Yes, in the study most people quote, with one catch that changes how you use it.

The work was done at New Bolton Center, University of Pennsylvania, by Michaela Kristula and Sue McDonnell. Kristula described it in an EQUUS Q&A: 14 pony stallions, stabled in winter with the barn between about minus 7 and 5°C (19 to 41°F), were offered warm water in one period and near-freezing water in another. Across both trials, the ponies drank 40 percent more when their water was warm.

• Heated buckets averaged about 19°C (66°F).
• Cold water sat at about 0 to 1°C (32 to 34°F) when refilled.
• Most drinking happened within three hours of feeding and refilling.

The catch: when the ponies were offered warm and cold side by side, more of them chose the cold water. So the warm bucket works when it is the only bucket. Hanging a warm one next to an icy trough may not change much.

Kristula’s practical suggestion was water kept continuously at roughly 20 to 35°C (68 to 95°F), or buckets filled twice a day at feed times with hot tap water of about 46 to 49°C (115 to 120°F), which had cooled to that 20 to 35°C range by the time the ponies did most of their drinking. In most UK yards that means a hot tap or a kettle for the morning and evening buckets.

How can you tell if your horse is not drinking enough?

Look at the water and look at the droppings. Those two tell you more than anything you can do with your fingers.

• Water left over. Buckets fuller than usual in the morning, or a trough that hasn’t gone down, are the earliest clue.
• Droppings. The BHS lists a reduced number of droppings, or drier droppings, as a common sign of impaction colic. Count the piles in the stable or the paddock corner you know, and notice if they look smaller, harder or drier than normal.
• Eating less. The MSD manual links poor water access to lower feed intake.

What about the skin pinch? It is widely taught, and the evidence for it is poor. A 2008 study from the Brooke and the University of Bristol measured 50 working horses as they rehydrated and found the standardised skin tent test, and gum dryness, were not valid or repeatable indicators of dehydration. Its conclusion was that how much a horse drinks is the most reliable guide. Those were working horses in heat in Pakistan, not a UK yard in January, but it is a reason not to trust a quick pinch.

How do you measure how much your horse drinks?

Buckets are the easy case. Know your bucket’s volume, fill it to the same mark each time, and note how many you fill and how much is left. Two buckets in, half of one left in the morning, is a number you can write down.

Troughs are the hard one. A shared field trough tells you what the group drank, not your horse, and a self-filling one tells you almost nothing. If a horse on a trough worries you, the practical fix is to bring it in and offer buckets for a day or two so you can see what it actually takes.

Automatic drinkers have the same problem: they refill as the horse drinks, so there is nothing to count unless the drinker has a meter.

Whatever you use, write it down for a few normal days first. A baseline is what makes a drop visible.

How do you keep a horse drinking in winter?

• Break the ice, and take it out. In freezing weather World Horse Welfare advises checking troughs and buckets two or three times a day to break and remove the ice. Twice a day is the minimum when there is a hard frost.
• Take the chill off. Warm water to the morning and evening buckets, and offer the warmed water instead of, not alongside, icy water.
• Add water to the feed. Soaked hay, soaked hay cubes, soaked sugar beet or a sloppy feed all put water in through the mouth without the horse having to choose to drink it.
• Salt. The MSD manual recommends a free-choice source of salt because most concentrate feeds do not provide enough. A lick in the stable or field is the simple version.
• Keep it clean. The BHS lists dirty water as a reason horses drink less. Scrub buckets, and clear leaves and slime from troughs.
• Watch the pecking order. A low-ranking horse may be kept off a shared trough. Two water points help.

When should you call the vet about a horse not drinking?

Ring your vet if your horse:

• Has stopped drinking, or is clearly drinking far less than its normal
• Is passing fewer or no droppings, or the droppings are dry and hard
• Shows any sign of colic: restlessness, pawing, looking round at its flanks, lying down more than usual or rolling
• Is off its food as well as its water
• Is dull and quiet, or its pulse is raised at rest

The BHS says colic can deteriorate quickly and should be treated as an emergency, and its REACT campaign with the University of Nottingham asks owners to contact the vet as soon as they notice changes. I looked for a sourced figure for how many hours a horse can go without drinking before you should call, and did not find one I would stand behind. So there isn’t a number to wait for. A horse that has not drunk overnight and is passing fewer droppings is a phone call, not a wait-and-see.

If you can, take a temperature, pulse and breathing rate before you ring, and listen for gut sounds. Our guide to normal horse temperature, pulse and respiration shows how, and the vet will want those numbers.

Where the technology fits

A bucket, a jug and a pen are the real tools here. An app helps with the part people stop doing after a week: writing it down.

In Stride, each horse has a hydration card on its profile. You log a drink with a full bucket button (counted as 15 litres), a half bucket button, or by typing the litres yourself, and you can go back and fill in a day you missed. The card shows today’s total against a guide of about 30 litres, and a bar chart of the last seven days. Water is always in litres, even if you use hands and pounds elsewhere in the app. Logged drinks also appear on the horse’s health timeline.

Two other parts of the app read those logs:

• The Genome health score includes a hydration marker, but only once you have logged water on at least three of the last seven days. It averages the days you logged and compares that with the ~30 litre guide. It stays silent on sparse logging, because logged buckets under-count trough drinking.
• Rein, the AI assistant, is given today’s total and a seven-day average, and is told to point out a sudden drop or spike without diagnosing anything.

You can also log not drinking and signs of colic as observations, each with a mild, moderate or marked severity, so they sit on the same timeline as the water log.

What it does not do: there is no alert when intake falls, no notification for a missed day, and no reading of troughs or automatic drinkers. The 30 litre guide is one figure for every horse, not a target worked out for yours, and a 350 kg pony on grass will rightly sit below it. It is a record, and the judgement stays with you and your vet.

If you take one thing from this: this week, before the first hard frost, count your horse’s buckets for three normal days. When the water starts freezing, you will know what normal looks like.