📖 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:
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Enter your livestock numbers
Count each animal type on your property. Leave a field at zero if that animal type is not present. The calculator uses standard FAO daily water consumption rates per head.
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Enter your irrigated area and crop type
Select the unit (hectares or acres) and pick the crop type that best matches your operation. Irrigation water demand varies significantly by crop — greenhouse crops can need 10× more than pasture.
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Set reserve storage days
Drag the slider to select how many days of water supply you want to hold in reserve. For farms relying on a pump or bore, 3–7 days is typical. Drought-prone regions should plan for 10–14 days.
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Click Calculate
The calculator shows your total daily water demand (livestock + irrigation), the recommended tank capacity in litres and US gallons, and a visual breakdown of demand sources.
Tip: Add 15–20% to the recommended size for waste, system losses, and unexpected demand spikes during heat events. A buffer above the calculated figure is always worth it.
📐 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) × Crop Daily Water Use (mm/day) × 10,000 ÷ 1,000
Tank Size (L) = Total Demand × Reserve Days
Daily water use per head is sourced from FAO Irrigation and Drainage Paper No. 33 and USDA extension guidance. Irrigation water use is expressed as mm/day of water depth over the irrigated area.
Daily Water Rates Used
| Animal | L/head/day | Source |
|---|
| Cattle (beef/dairy) | 50–80 L (avg 65) | FAO / USDA |
| Horses | 40–70 L (avg 55) | FAO / USDA |
| Pigs / Hogs | 15–25 L (avg 20) | FAO |
| Sheep / Goats | 5–15 L (avg 10) | FAO |
| Poultry (chicken) | 0.3–0.5 L (avg 0.4) | USDA |
Irrigation Daily Water Use by Crop
| Crop Type | Typical mm/day | L/ha/day |
|---|
| Cereals / Grains | 3–5 mm/day | 30,000–50,000 |
| Vegetables | 4–6 mm/day | 40,000–60,000 |
| Fruits / Orchards | 3–6 mm/day | 30,000–60,000 |
| Pasture / Forage | 2–4 mm/day | 20,000–40,000 |
| Cotton / Sugarcane | 5–8 mm/day | 50,000–80,000 |
| Greenhouse crops | 6–10 mm/day | 60,000–100,000 |
❓ FAQ
Frequently Asked Questions
How do I calculate farm water storage requirements?
Add up daily livestock demand (head count × per-animal rate) plus irrigation demand (hectares × daily crop water use in mm × 10). Multiply the total by the number of reserve days you want to store. This calculator automates all those steps for you.
How much water does a cow drink per day?
A beef or dairy cow drinks approximately 50–80 litres per day, with the average around 65 L. Lactating dairy cows in hot weather can consume up to 100 L/day. This calculator uses a conservative 65 L average, so adjust your reserve days upward in hot climates.
How many days of reserve should a farm water tank hold?
Standard practice is 3–5 days for farms with reliable mains or bore water. Farms in drought-prone regions or those relying on seasonal rain should plan for 7–14 days. Emergency planning guidelines in many countries recommend a minimum of 3 days' supply at all times.
What is the water requirement for irrigation per hectare?
It varies significantly by crop. Pasture and forage require 20,000–40,000 litres per hectare per day; vegetables need 40,000–60,000 L/ha/day; and water-intensive crops like cotton or sugarcane can exceed 80,000 L/ha/day. This calculator applies mid-range FAO figures for each crop category.
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?
Not automatically — it calculates demand-based storage. Add 10–20% to the result to cover irrigation system losses, tank evaporation (particularly for open dams), and animal waste. Covered tanks lose far less water than open dams in hot climates.
What size tank do I need for 50 cattle with 5 acres of vegetables?
50 cattle × 65 L/day = 3,250 L/day. 5 acres ≈ 2.02 ha × 50,000 L/ha/day = 101,000 L/day. Total daily demand ≈ 104,250 L. With a 3-day reserve, you need roughly 312,750 litres (about 83,000 US gallons). For a 7-day reserve, plan for 730,000 L.