Enter your livestock counts, irrigated acreage, and crop type to get the total daily water demand and recommended storage tank size — in litres and gallons.
Livestock + irrigation + buffer
Days of reserve storage
Litres, gallons, m³
Works on any device
Livestock rates from OMAFRA, crop water from FAO-56
⚠ Please enter at least one livestock count, other daily use, or an irrigated area with a crop type.
WaterTankCalculator.com — Farm Water Storage Results
Your Results
Total Storage Needed
—
Litres (L)
Daily Demand
— L/day
Livestock Need
— L/day
Irrigation Need
— L/day
Reserve Days
— days
US Gallons
— gal
Cubic Metres
— m³
Livestock Storage
— L
Irrigation Storage
— L
Suggested Tank to Buy
— L
Storage Breakdown
📖 How To Use
How to Use the Farm Water Storage Calculator
Sizing a farm water storage tank correctly prevents costly shortfalls during dry spells. Follow these steps:
Enter your livestock numbers
Count each animal type and pick the class that matches most of them — a milking dairy cow drinks about three times what a dry cow does. Leave a field blank if you don't keep that animal. Daily rates come from the Ontario Ministry of Agriculture (OMAFRA) livestock water factsheet. Tick "hot weather" if your summers are hot.
Enter your irrigated area and crop type
Select the unit (hectares or acres), pick the crop type, and enter your peak-month ETo if you know it (blank uses 6 mm/day). Choose your irrigation method so system losses are included. Irrigation usually dwarfs livestock use — one hectare at peak can need more water in a day than 1,000 beef cows.
Set reserve storage days
There are two sliders. Livestock reserve covers animals and other essential use — 3–7 days is common on a single bore or pump, 10–14 in drought-prone areas. Irrigation reserve is usually shorter (often 1–3 days, or 0 if you pump straight to the field), because crops can ride out a short gap and storing days of irrigation water gets very large.
Click Calculate
The calculator shows daily demand split into livestock and irrigation, the storage each needs, the total in litres, US gallons and m³, and a suggested tank to buy with a 15% margin, rounded up to a typical size.
Tip: The suggested tank already adds 15% for water below the outlet you can't use and for trough spillage. Irrigation system losses are already included through the method you pick. For open dams and ponds, also allow for evaporation, which can take several millimetres of depth a day in hot weather.
📐 The Formula
Farm Water Storage Formula Explained
The calculator combines livestock and irrigation demand, then multiplies by reserve days:
Total Demand (L/day) = Livestock Demand + Irrigation Demand
Livestock Demand = Σ (Animal Count × Daily Rate per Head)
Irrigation Demand = Area (ha) × (Kc × ETo ÷ Efficiency) (mm/day) × 10,000 Storage (L) = Livestock Demand × Livestock Days + Irrigation Demand × Irrigation Days
Tank to buy = Storage × 1.15, rounded up to a typical size
Daily water use per head comes from the Ontario Ministry of Agriculture, Food and Rural Affairs factsheet Water Requirements of Livestock (No. 23-023, 2023), cross-checked against North Dakota State University's AS1763. Irrigation demand is crop water use from FAO-56 (Kc × ETo) divided by the efficiency of your irrigation method. One millimetre of water over one hectare is 10,000 litres.
Daily Water Rates Used
Animal
Average L/head/day
Range (hot weather = top)
Dairy cow, milking
115
68–155 (rises with milk yield)
Dairy cow, dry
41
34–49
Dairy heifer (5–24 mo)
25
14–36
Beef cow with calf
55
43–67
Beef dry cow / bull
38
22–54
Feedlot steer (364–636 kg)
41
27–55
Horse (~1,000 lb)
32.5
26–39
Finisher pig (70–110 kg)
9
7.3–10
Lactating sow + litter
20
18–23
Lactating ewe + lambs
10
9–10.5
Laying hen
0.25
0.18–0.32 (+50% above 30 °C)
Broiler (summer)
0.45
up to 0.77 at 5–8 weeks, 32 °C
Source: OMAFRA Factsheet 23-023, Water Requirements of Livestock (2023), Tables 1–8. Poultry figures are per 1,000 birds in the source and shown here per bird. Goats are not listed separately; sheep values are used as an approximation for goats of similar size.
Irrigation Daily Water Use by Crop
Crop Type
Kc mid
Crop use at ETo 6 (mm/day)
Drip, L/ha/day
Sprinkler, L/ha/day
Cereals / Grains
1.15
6.9
76,700
92,000
Vegetables
1.10
6.6
73,300
88,000
Fruits / Orchards
0.90
5.4
60,000
72,000
Pasture / Forage
0.95
5.7
63,300
76,000
Cotton / Sugarcane
1.20
7.2
80,000
96,000
Kc mid values are representative of each group in FAO-56 Table 12 (for example wheat and barley 1.15, small vegetables 1.05 and tomato 1.15, apples without ground cover 0.95 and citrus 0.65, grazing pasture 0.85–1.05, cotton 1.15–1.20 and sugarcane 1.25). These are peak-season figures, which is what storage should be sized for. At ETo 4 mm/day, multiply by 0.67. For a single crop and growth stage, use the Crop Water Need Calculator.
🌾 Use Cases
When Farmers Use This Calculator
🐄
Livestock Operations
Cattle, dairy, and mixed farms sizing tanks to ensure continuous supply during pump failures or dry seasons.
🌽
Crop Irrigation Planning
Growers planning drip or sprinkler systems need to know how much water storage backs up each irrigation run.
🌧️
Rainwater Harvesting
Farms supplementing mains water with roof catchment use storage sizing to bridge rain-free periods.
💧
Bore/Pump Sizing
Knowing peak daily demand helps right-size pumps and borehole infrastructure to match storage drawdown.
🔥
Drought Resilience
Farms in high-risk areas use extended reserve buffers (10–14 days) to protect animals through supply disruptions.
🏗️
New Farm Build-outs
Agricultural project planners and engineers use this to specify tank volumes at the infrastructure design stage.
⚖️ Design Note
Livestock vs Irrigation Storage: Plan Them Separately
On most mixed farms, irrigation is 90% or more of daily water use, but livestock water is the part you cannot go without. Animals cannot go long without water: cattle suffer within a day or two in hot weather, and a milking cow's yield drops as soon as she is short of water. Crops are more forgiving — at full canopy a day or two without irrigation is drawn from soil moisture.
That is why this calculator has two reserve sliders. Sizing everything to the same number of days either leaves the animals under-protected or pays for a very large irrigation tank you rarely use. A common pattern is a covered tank holding 7 days for livestock and the house, plus a pond, dam or day tank for irrigation sized to 1–3 days of peak use or to the pump's refill rate.
Keep the livestock reserve on its own outlet or set higher than the irrigation draw-off, so an irrigation run can never empty the animals' water.
🧮 Worked Example
Worked Example: Dairy Farm With 2 Hectares of Vegetables
40 milking dairy cows, 10 dry cows, 300 laying hens and 2 ha of drip-irrigated vegetables, on a single borehole. Peak ETo is 6 mm/day.
Item
Working
L/day
Milking cows
40 × 115 L
4,600
Dry cows
10 × 41 L
410
Laying hens
300 × 0.25 L
75
Livestock total
—
5,085
Vegetables
2 ha × (1.10 × 6 ÷ 0.90) mm × 10,000
146,667
Using the same 5-day reserve for everything gives 758,758 L of storage, and about 875,000 L to buy. Splitting it — 7 days for the livestock (35,595 L, so a 41,000 L tank) and 2 days for irrigation (293,333 L, about 340,000 L of pond or tank) — protects the animals for longer with well under half the total storage. In hot weather the livestock figure rises to about 6,800 L/day, which is worth checking with the hot-weather box before you order.
❓ FAQ
Frequently Asked Questions
How do I calculate farm water storage requirements?
Add up daily livestock demand (head count × litres per head per day for that class of animal). Work out irrigation demand as hectares × crop water use in mm/day × 10,000, where crop water use = Kc × ETo ÷ irrigation efficiency. Multiply each by the number of reserve days you want for it, add them, and allow about 15% extra when you buy the tank. This calculator automates all of those steps.
How much water does a cow drink per day?
It depends on the type of cow. A milking dairy cow drinks about 115 litres a day on average, ranging from roughly 68 L to 155 L as milk yield rises — high-yielding cows drink the most. A dry dairy cow drinks about 41 L, a beef cow with a calf about 55 L (43–67 L), and a dry beef cow or bull about 38 L. All of these rise in hot weather. Figures are from OMAFRA Factsheet 23-023.
How many days of reserve should a farm water tank hold?
For livestock, 3–5 days is a common choice on a reliable mains or bore supply, and 7–14 days in drought-prone areas or where you depend on one pump or on carted water. Base it on how long a breakdown could realistically take to fix. Irrigation reserve is usually much shorter — often 1–3 days — because crops can draw on soil moisture for a short gap and storing many days of irrigation water becomes very large.
What is the water requirement for irrigation per hectare?
One millimetre of water over one hectare is 10,000 litres. At peak season most crops use about 5–7 mm/day in a hot, dry climate (FAO-56 Kc × ETo at an ETo of 6 mm/day), which is 50,000–70,000 L/ha/day at the plant. Irrigation losses push the amount you must store higher: about 60,000–80,000 L/ha/day with drip and 72,000–96,000 L/ha/day with sprinklers. In cooler or humid climates the figures are lower.
Can I use this calculator for a mixed livestock and crop farm?
Yes — enter your livestock counts and your irrigated acreage simultaneously. The calculator adds both demand streams together before multiplying by reserve days to give you a combined total tank size recommendation.
Does this calculator account for evaporation or system losses?
Irrigation system losses are included — the method you pick (drip, sprinkler or surface) divides crop water use by its efficiency. The suggested tank to buy adds 15% for the water below the outlet and trough spillage. Evaporation from an open dam or pond is not included; in hot weather it can remove several millimetres of depth a day, so covered tanks are better for livestock reserves.
What size tank do I need for 50 cattle with 5 acres of vegetables?
Take 50 beef cows with calves at 55 L each, which is 2,750 L/day. Five acres is 2.02 ha. Drip-irrigated vegetables at peak (Kc 1.10 × ETo 6 mm ÷ 0.90) need about 73,300 L/ha/day, or 148,385 L/day. That is 151,135 L/day in total. With 3 days of reserve for both, you need about 453,000 litres (about 120,000 US gallons), so buy around 525,000 L. The livestock share is under 2% of that. Seven days for the cattle (19,250 L) plus 2 days for irrigation (296,770 L) is a better split for most farms.
✅ Sources & Review
Sources and review
The livestock rates, crop water use and efficiencies on this page come from these references:
OMAFRA Factsheet 23-023: Water Requirements of Livestock — Ontario Ministry of Agriculture, Food and Rural Affairs (2023). Daily litres per head for dairy, beef, horses, swine, sheep and poultry, and the +50% poultry increase above 30 °C.
The 15% purchase margin and size rounding are engineering practice rather than a published standard. Use your supplier's actual tank sizes when you order.
Reviewed by John Mac, PE, Water Systems Specialist
Texas-licensed Professional Engineer with 13+ years in residential water storage and 180+ tank projects. John writes and reviews every calculator on this site.
