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Horse Water Calculator (Daily Intake by Weather & Work, Trough Size, Refill Time, Heater Watts)

Estimate how much water your horses drink per day from body weight, temperature, work and diet, size a trough or automatic waterer so it holds a day or two, see how long a hose takes to fill it, the freeze-protection heater wattage and its running cost, and the signs of dehydration to watch.

Horses sharing the trough
Average body weight
Daytime high temperature
Work level
Diet
Trough capacity
Hose flow
Winter overnight low
Electricity price
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How it works

base ≈ 1 gal per 100 lb body weight per day (mild weather, hay diet) · × heat (≤ 40 °F 0.85; 65 °F 1.0; 80 °F 1.2; 90 °F 1.5; hotter 1.9) × work (idle 1.0; light 1.15; moderate 1.4; heavy 1.8; lactating 1.7) × diet (hay 1.0; mixed 0.8; lush pasture 0.55) · trough days = capacity ÷ herd daily; fill time = gallons ÷ gpm · de-icer ≈ 0.9 W per gallon per °F below freezing (250–1,500 W)

A horse drinks roughly a gallon per hundred pounds of body weight in mild weather on a hay diet, and that swings enormously: heat, work and lactation can double it, while lush pasture — which is mostly water — halves it. From the daily need the calculator sizes a trough that holds a day or two (fresh but not stale), tells you how long the hose takes, and in winter estimates the de-icer wattage and its electric bill, because cold water and frozen troughs are the classic cause of winter impaction colic. The point is that water is the cheapest thing you feed and the most dangerous to run short of.

Worked example

Three 1,100 lb horses in light work at 75 °F on hay drink about 15 gallons each — roughly 46 gallons a day. A 100-gallon trough holds just over two days for the group and takes 17 minutes to fill with a 6 gpm hose (about 8 minutes of topping up daily). At an overnight low of 15 °F it needs a 1,500 W thermostatic de-icer, roughly 450 kWh and $71 a month.

Frequently asked questions

How much water does a horse drink a day?

Typically 5–10 gallons for an idle 1,000–1,200 lb horse in mild weather, 12–20 in heat or work, 15–20 for a lactating mare, and as little as 3–5 on lush pasture. Feed hay dry and the horse drinks more; soaked hay or grass supplies part of the need.

What size water trough for horses?

Enough for one to two days: about 15 gallons per horse per day, so a 100-gallon trough for three to five horses. Bigger troughs go stale in summer; several smaller waterers spread across a big herd prevent a dominant horse blocking access.

Do I need a trough heater?

Wherever nights drop below about 25 °F, yes: horses reduce intake when water is near freezing and cannot drink through ice, and winter colic follows. A thermostatic de-icer (250–1,500 W by trough size and climate) or an insulated automatic waterer keeps water 40–50 °F; use a GFCI and check for stray voltage.

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Equine figures are planning estimates from common husbandry references (NRC 2007, extension services). Individual horses, forage quality, climate and workload vary — weigh hay, body-condition score regularly and work with your vet, farrier and nutritionist.