Farm Water Security Calculator
Assess your farm's water security: total stored water, daily consumption from livestock, household use, and irrigation, and how many days your supply will last.
Results
How to Use This Calculator
Enter dam storage (ML), water tower storage (ML), bore/well flow in litres per day, cattle and sheep numbers, household water use in L/day, irrigated area in hectares, and typical irrigation depth per event in mm. Click Calculate for your water security status.
About This Tool
The Farm Water Security Calculator helps farmers understand their true water balance. It accounts for all demand sources — livestock drinking water, household use, and irrigation — against all supply sources: dam storage, tower storage, and well replenishment. This reveals hidden shortfalls before they become emergencies.
Applicability: Suitable for irrigation planning in North America and Europe, adaptable to semi-arid and Mediterranean climates worldwide.
How the Calculation Works
Total storage = (Dam + Tower) in ML converted to litres. Daily use = Cattle × 80 L + Sheep × 12 L + Household + (Irrigated area × irrigation depth × 10 m³/ha-mm ÷ 7 days). Net daily draw = Daily use − Well flow. Days of supply = Total storage ÷ net daily draw. Status bands: 90+ days = Good, 30-90 = Caution, 14-30 = Warning, <14 = Critical.
Real-World Example
5 ML dam + 0.5 ML tower = 5.5 ML total. 50 cattle × 80 L = 4,000 L; 100 sheep × 12 L = 1,200 L; household 500 L; irrigation (2 ha × 25 mm × 10 ÷ 7) = 7,143 L/day. Total daily = 12,843 L. Well adds 5,000 L. Net draw = 7,843 L/day. Days = 5,500,000 ÷ 7,843 = 701 days. But with 8% monthly evaporation, plan for 500 days — and cut irrigation early in a dry spell.
Common Mistakes & Tips
Common mistakes: ignoring evaporation from open dams (5-10 mm/month in dry climates), forgetting that well flow drops during drought (lower water table), not accounting for livestock growth (calves grow into drinkers), and not planning a trigger point to stop irrigation and buy supplemental feed.
Reviewed by Agricalc Editorial Team — Agricultural engineers and agronomists with 10+ years of field experience. Our team verifies every calculator formula against peer-reviewed extension publications. For site-specific advice, consult your local agronomist.
References
- USDA NRCS — Farm Water Management
- FAO — Farm Water Supply and Demand
- Penn State Extension — Farm Water Planning
Frequently Asked Questions
How much water does a cow drink per day?
A mature beef cow drinks 30-50 L/day in cool weather and 60-100 L/day in hot weather (over 30°C). Lactating dairy cows drink 70-120 L/day. The calculator uses 80 L/day as a warm-weather average. Always plan for peak summer demand, not annual average. Calves drink 10-20 L/day and grow into full intake within 12-18 months.
How do I calculate effective storage accounting for evaporation?
Subtract evaporation loss from your storage each month. In hot climates, open water surfaces lose 5-10 mm/day (150-300 mm/month). For a 1,000 m² dam, that's 150-300 m³ (0.15-0.3 ML) per month. The calculator doesn't include this — you should mentally reduce days of supply by evaporation rate. Deep, narrow dams lose less than shallow, wide ones.
When should I stop irrigating and switch to feeding?
Set trigger points: when dam storage drops below 50%, reduce irrigation frequency; below 30%, stop irrigation entirely and switch livestock to dry feed/hay. This preserves drinking water for the herd. Many farmers lose livestock because they keep irrigating lucerne until the dam is nearly empty, then have no drinking water. Plan the cut-off before the dry season starts.
Does my well/bore flow decrease in dry years?
Yes, significantly. Bore yields often drop 30-60% during drought because the water table falls. A bore that produces 5,000 L/day in wet years may produce only 2,000 L/day in dry years. Always use your worst-case (drought) flow figure for planning, not your best wet-season flow. Test the bore at the end of the dry season each year.
How many days supply should I aim for?
Aim for at least 90 days of reserve supply (3 months) for livestock-only operations, and 180 days if you rely on irrigation. In drought-prone regions, target 365 days. If your calculation shows under 60 days, it's time to: reduce stock numbers, drill a new bore, add a dam, or arrange for water trucking contracts in advance.
