CASTLE FEEDS – Water, the forgotten nutrient…

The right nutrition is essential to keep your eventer happy, healthy and performing well and good nutrition revolves around including the correct levels of nutrients. There are six so-called ‘essential’ nutrients in the horse’s diet: carbohydrates, fats, protein, vitamins, minerals and water –  yet water is easily the most essential. Despite its importance, water is frequently overlooked when considering a horse’s dietary needs and is often referred to as the ‘forgotten nutrient’, when it should be the main one. 

Lisa Elliott MSc – nutritionist at Castle Horse Feeds – gives us some insights into why water is so important and how to make sure your horse is drinking enough.

Why is water so important? 

Well for a start, neither we or our horses could survive without it! Horses can survive up to 90 days without food but without water it is just 7 days. In mature horses, total body water comprises 61-72% of bodyweight (BW) and in foals it is estimated at 66-84% BW, demonstrating just how important water is within the body. 

Water is directly or indirectly involved with virtually every physiological process essential to life including circulation, digestion, lymphatic system, excretion (urine, faeces, tears and mucus), and thermoregulation. Full water hydration is therefore, vital for optimal body function and performance when competing and if a horse becomes even a little dehydrated, body function becomes compromised. Dehydration is a serious condition which can be potentially life-threatening so it’s essential to make sure your horse is getting enough water to meet their needs. You can check if your horse is at all dehydrated by carrying out a simple skin pinch test. 

To meet water requirements within the body, an optimum water balance needs to be reached between water input and water output. 

Water input comes from drinking water, feed and metabolic processes. All feeds contain water and the water content depends on the source of that feed. Hay and grain contribute very little to the water input but haylage (32-45% moisture) can supply about 25% of water input and fresh grass which can typically be 60-80% moisture can almost satisfy water requirements! Metabolic water is that which is generated from the metabolism of carbohydrates, fats and proteins and is estimated to contribute about 11-13% of daily water requirements.  Water output or loss is a result of faeces, urine, sweating and respiration. 

Daily water requirements at maintainance are estimated at about 5 litres per 100 Kg BW, but when working hard in hot conditions this can increase quite significantly to around 12-15L/100 kg BW. Water intake from feed and drinking must, therefore, be sufficient to replace what is lost and meet requirements.

Water Intake

Water intake is essential to keep the body functioning well and avoid the detrimental effects of dehydration. Water intake and the amount a horse will drink is influenced by: 

Body Size/Weight  

Body size and weight influences the water capacity if a horse so larger horses generally have a greater requirement for water than smaller ponies 


The dry matter (DM) content of feeds will influence the amount of water your horse drinks.  Horses receiving forage containing a higher DM, for example, will typically drink more than those out at grass getting a large part of their water requirements satisfied by its higher water content, who will typically drink less.


Water intake rises with temperature and there is a positive link between ambient temperature and water intake which is an important consideration when eventing in the heat of summer!!  


Water becomes even more essential when a horse is working regularly throughout the eventing season. A higher workload will mean a greater water intake compared to a lighter workload or maintenance. Moderate work, for example, can increase water intake about 40% above that of a horse at maintenance. So, when training and competing in eventing it’s important to ensure your horse has access to as much water as they want.


Foals have a greater water intake for their size than mature horses.  Older horses on the other hand tend to drink less so will have a decreased water intake. If you are lucky enough to have an older schoolmaster, it’s essential to make sure that they are getting enough water to be able to perform their best. 


Water intake can be impacted by certain health problems. Chronic kidney disease or diarrhoea, for example, can cause increased water loses which must be replaced and these horses will need a greater intake of water. 

Any health condition that decreases feed intake, for example, gastric ulcers, can also decrease water intake. At the other end of the scale, certain metabolic conditions along with PPID (cushings) can promote excessive drinking and greatly increase water intake. 

Water Quality

The quality of your horses’ drinking water is important as poor-quality water can impact on health and discourage drinking.  Water should always be fresh, clean and palatable and delivered in buckets and troughs that are checked and cleaned regularly. Water, particularly in outside troughs, should be tested for chemical and bacterial contamination to provide your horse with a safe reliable source. 

Knowing how water intake is influenced is important to assess whether your horse is getting enough water and encouraging your horse to drink regularly when needed can help meet their requirements. 

Encouraging your horse to drink

The easiest way to encourage your eventer to drink regularly is by always providing constant access to fresh, clean and palatable water but there are some other ways to encourage sufficient water consumption:

  • Adding salt to the feed can help stimulate the thirst response and thus encourage drinking. 
  • Horses have been shown to prefer sweet solutions, so adding apple cordial, for example, to your horses drinking water, could help boost drinking. 
  • Buckets have been shown to be generally preferred by horses to smaller bowls so offering your horses water in a large bucket may help them to drink more. Additionally, using a bucket is great for measuring how much water your horse is drinking. 

Giving water at competitions

Water should always available to your horse during competitions and training to replenish what has been lost through exercise. Traditionally it was thought that you should withhold water from a horse when hot after strenuous exercise, for example just after a cross country round, for fear of inducing colic. However, this is a myth. There is no scientific evidence to support this idea and it is far more detrimental to the horse to let them get dehydrated and stressed which would cause colic, than allowing them to drink following exercise which is actually beneficial. 

Letting a horse drink gallons and gallons of water after strenuous exercise isn’t ideal just as it wouldn’t be for us to drink loads after running a marathon, for example. However, smaller, regular amounts of water immediately following exercise are essential to replace water losses and restore water balance within the body for optimum recovery. 

Winter Water 

With winter well on the way, it’s a good idea to think about maintaining your horse’s water intake because when the temperature starts to drop, horses are naturally inclined to drink less. Water troughs and buckets can become frozen when the temperature drops below freezing, so be aware of this and make sure ice is broken regularly on any frozen troughs. Adding hot water to warm the water above freezing has been shown to increase water consumption by 40%. so think about warming your horse’s water (ideally to between 7 – 18⁰C) to help increase drinking over the winter months. 

Water should be the primary nutrient for horses when considering their dietary needs. By being aware of what affects water intake, how much they are getting, and encouraging regular drinking throughout the year, you can help ensure your eventer stays hydrated and healthy for optimum performance. 

If you have any questions about creating the best diet for your horse and keeping your horse healthy through the right nutrition, please contact Lisa at Castle Horse Feeds –  

For more information see or call 01497 570345.

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