is this warm water or cold - I only ask cos when I was a holiday rep at least 3 of my clients died of a heart attack after jumping in the pool after getting hot in the sun
They endurance riders reckon the best way to cool down a horse is to wet it with lukewarm water, scape of the water, walk the horse around and soak with water and scrape off and second time, but I have never thought about putting cold water on a horse could bring on a heart attack unless the horse had an underlying heart weakness anyway.
QR
Water will heat up pretty quickly when put on the horse, that's why Eventers have Ice Cold Water and why you have to wash/scrape/wash/etc - to stop the insulating effect and actually causing the horse to overheat.
I think the reason the water has the chill taken off it is to stop the blood vessels constricting thereby slowing the cooling process.
When a child has a fever you are advised to sponge it using tepid water for the same reason.
i've heard of a man who had a heart attack and died after jumping in a cold swimming pool after working in a greenhouse for hours. big difference with wetting a horse, though, even with ice-cold water.. it wouldn't be anything like the shock of immersing it completely.
At race meetings I have been at the water they throw over the horses comes straight from a tap at the side of the paddock. It COULD be warm water but I doubt it.
The 10-15 minutes you are in the sauna will not raise your core temperature a hell of a lot, so when you jump in the ice cold water it feels like shock to the skin, but isn't a shock to the internal organs. However, when someone's core temperature gets severely high (heatstroke etc) then sudden immersion in cold water will cause muscles to spasm, including the heart, even in people who have otherwise healthy hearts.
To get the temperature down in an overheated horse (heatstroke etc rather than exercise) it is advisable not to throw cold water over the main part of the back as it can cause spasm - cold hosing under the tail is a better method, as the blood passes close to the skin at this point, so you are gradually, but effectively cooling the horse (same idea as running a cold tap over your wrists to cook you down).