Why does an arena surface need to stay moist?
Moisture holds the individual components of sand, fibre and rubber together, creating the cushioning and consistency a horse needs to work safely. Without adequate moisture, surface particles separate and dry out, causing dust, hard uneven footing, and faster breakdown of expensive surface materials. Too much moisture and the surface becomes boggy and unstable. The goal is consistent moisture throughout the full depth of the surface, not just the top layer, which is why surface-level sprinklers often fall short compared to sub-surface systems.
How to quickly check the water content of your riding surface? The ball test.
Apart from the obvious tell-tale signs of an under-watered or over-watered arena (such as dust or flooding) the simplest way to check the moisture content of your surface material is to take a handful of the surface and shape it into a ball. If the surface won’t bind together then it is likely to dry, especially if some dust is expelled. On the other hand, if the surface forms a muddy ball then it is too wet.
The surface should stick together so the ball holds its shape, but still be dry enough to crumble.
What moisture does to the arena surface
According to the FEI Equestrian Surfaces Guide water is the single most important factor that influences the properties you want from an arena.
"Moisture determines the properties of the sand, which in turn influences the functionality of the entire riding surface"
Beach sand analogy
Moist sand
Moisture binds the sand together making it easier to travel "over" the surface rather than "through it" because the surface supports your weight.
Dry sand
Your feet sink easily into the sand and it requires a lot more effort to maintain normal walking speed than in moist sand.
How does moisture change the sand?
When dry, sand is simply a collection of particles held together by friction. But once moisture seeps in, a fascinating transformation occurs. Depending on the type and size of the grains, water infiltrates the pores, creating adhesion between the particles. The adhesion means that the sand becomes firmer, able to support more weight and absorb impact.
How does water impact riding activities?
(This answer is reinforced by the following: White Paper on Equine Arena Surface Assessment)
Moisture content stands out as a crucial physical parameter to measure, as it significantly impacts the functional characteristics of a surface (Goodall et al., 2005; Peterson et al., 2008).
Research suggests that increased moisture content enhances particle adhesion, improves shear resistance and stability (Ratzlaff et al., 1997; Chateau et al., 2010; Murray et al., 2010a).
Optimal moisture is dependant on surface type and sport
However, once saturation occurs, there is a drop in shear strength. Typically, sand reaches its maximum shear strength between 8% and 17% moisture content (Barrey et al., 1991; Ratzlaff et al., 1997).
Optimal moisture levels vary depending on surface type and sport. For instance, gaining maximum shear strength may not be ideal for actions like the spin in reining horses, as it could increase limb loading by reducing hoof rotation ability, necessitating a slightly drier surface to mitigate injury risks.
Studies show that low and high moisture contents result in higher peak forces on a sand surface, compared to a moderate moisture content. The higher peak forces are likely due to the formation of a hard base layer where the hoof penetrates to the base (Ratzlaff et al., 1997). Therefore consistent moisture management is very important to every sport.
Changes is surface hardness are linked to moisture and compaction
Even a slight variation in moisture content can significantly impact peak vertical deceleration during the stance phase (Chateau et al., 2010). Research shows that surface hardness is a result of low moisture content and therefore an increase in compaction.
More awareness and understanding of moisture effects to riding surfaces is needed
Understand your sand! Factors influencing sensitivity to moisture content encompass particle size, resulting pore sizes, and sand type, which can affect surface chemistry and water attraction to sand particles. Ultimately our riding experience and future with horses is somewhat dependant on providing the optimal riding surfaces.
What happens when moisture goes wrong?
Just like other surface components, water is a vital component of an arena footing and needs to be added back in when the surface dries out.
Arena irrigation is so important for a variety of your surface’s properties:
Safety
A surface that is lacking moisture may be unstable and inconsistent. Not only does this make the surface less safe to ride on, as it increases the risk of accidents and injuries, but it can actually make a young or nervous horse feel unsure of himself, as we expect them to listen to our aids while also navigating an inconsistent and uncomfortable surface.
Dust Suppression
Not only does dust look dirty, but it can impede breathing for both horses and riders. A dust-free environment is much healthier for horses and riders and is especially important for those who already suffer from breathing problems. A well-watered arena helps to bind the dust particles to the surface, so it does not become airborne and affect breathing. This tends to be more of an issue with older or particularly fibrous surfaces
Hoof Support
When water is added to the arena surface, the material particles absorb the water, causing them to swell and bind to each other. This creates a cushioned effect and allows the surface to absorb some of the impact made by the horse’s hooves, which reduces the impact on both the arena base, as well as the horse’s joints and tendons.
Surface Materials
When the surface becomes too dry, the materials start to separate. Arena surfaces are a huge investment, so it is worth putting in the extra effort and resources to keep the materials properly mixed so the surface can work as it was designed to.
Riding on a dry surface can also reduce the longevity of the surface, as the hooves break down the materials more easily, so it becomes powdery and therefore more dusty to ride on.
What does poor moisture management mean for your horse?
The consequences of poor moisture management land directly on the horse. Every ride on a poorly moistened surface creates cumulative stress that is easy to miss until it becomes a soundness problem.
A dry, compacted surface increases impact forces
When moisture drops below the optimal range, sand loses its adhesive properties and the surface hardens. Studies show that both low and high moisture contents produce higher peak forces on the hoof at landing compared to a correctly moistened surface (Ratzlaff et al., 1997). On a hard, compacted surface those forces transfer directly into the hoof, fetlock, tendons and joints rather than being absorbed by the surface material. For horses in regular work this is a cumulative loading problem - each individual stride may seem fine but the effect compounds over weeks and months.
An inconsistent surface creates uneven loading
Dry patches alongside wetter areas - the typical result of overland sprinkler systems or irregular manual watering - create a surface that behaves differently underfoot from stride to stride. The horse adjusts its movement to compensate, which leads to asymmetric muscle loading and over time can contribute to uneven muscle development and compensatory movement patterns. In jumping or fast work, an unexpectedly dry patch underfoot is an acute injury risk rather than just a long-term welfare concern.
Dust is a respiratory issue, not just a visibility one
When surface moisture drops, fine particles become airborne with every stride. In an enclosed indoor arena this creates a sustained respiratory challenge for horses and riders. For horses with existing respiratory sensitivity, a consistently dry surface is a management problem that no amount of stable ventilation fully compensates for.
Too much moisture wastes water and disrupts consistency
Overwatering a sand surface does not typically make it boggy - the drainage characteristics of correctly specified arena sand mean excess water passes through rather than pooling. The real problem with overwatering is waste: water that runs off or drains before it can be absorbed by capillary action does nothing for surface consistency and drives up consumption unnecessarily. Inconsistency remains the core issue regardless of direction - too dry and the surface hardens, too wet and you are irrigating without benefit. The goal is maintaining the optimal moisture range consistently, which manual systems struggle to do reliably across a full arena surface.
For a detailed breakdown of how surface conditions interact with each phase of the horse's stride, see our guide to the 3 phases of footfall and riding surfaces.
Managing moisture consistently
Understanding why moisture matters is the first step. The next is choosing a system that maintains it consistently at depth across the full arena surface - not just the top layer after a spray. Manual watering with a bowser, hose or basic sprinkler will always leave drier patches, wetter patches, and a surface that dries faster at the top than the base.
Now you understand why moisture matters, the next question is which system will maintain it consistently. We cover the ArenaMate® irrigation options - AquaOver, AquaUnder and HIT Active-Aqua - in our Arena Irrigation Systems guide.
Now you understand why moisture matters, the next question is which system will maintain it consistently. We cover the ArenaMate irrigation options here: