Enter your household size, climate zone, and activity level to get your total daily water requirement — in litres, gallons, and a per-person breakdown.
Fill in your household details — results update instantly
Household details
Adults
Children
Climate
Lifestyle & storage preferences
Activity Level
Comfort Level
Buffer Days
⚠ Please enter at least 1 adult and a valid number of buffer days (1–30).
WaterTankCalculator.com — Daily Water Requirement Results
Your Results
Total Daily Requirement
—
Litres per Day (L/day)
Per Person / Day
— L/person
US Gallons / Day
— gal/day
UK Gallons / Day
— gal/day
Weekly Total
— L/week
Monthly Total
— L/month
Recommended Tank
— L
Daily Usage Breakdown
Recommended Tank Fill Level (Buffer Days)
📖 How To Use
How to Use This Calculator
Find your household's daily water requirement in four quick steps:
Enter the number of adults and children
Children under 12 usually use less water than adults — shorter showers, smaller drinks and meals. The calculator counts each child as 65% of an adult, a planning assumption; if your children use as much as adults, enter them as adults.
Select your climate zone
Heat raises drinking, bathing and garden use, but not toilet flushing or laundry. The calculator raises only those climate-sensitive uses: by 40% for hot/arid, 20% for tropical/humid, and lowers them 10% for cold climates. These are planning factors, not measured averages.
Choose your activity level and comfort standard
"Minimum" uses 50 L per person per day — the level the WHO calls intermediate access, enough for drinking, cooking and basic hygiene. "Basic" is 80 L, "Standard household" 130 L, a typical piped home with water-efficient fittings, and "High comfort" 200 L with garden watering. For comparison, US homes average about 310 L (82 gallons) per person per day, according to US EPA WaterSense. Activity adds 8 L (moderate) or 20 L (high) per adult for drinking and extra washing.
Set your buffer days
This sets how large a tank you need: the number of days your stored water should last without any supply. A few days covers short interruptions; areas with supply on alternate days or frequent outages often plan for a week or more.
Tip: The "Recommended Tank" already includes 15% extra over the water you need, because a tank cannot deliver its last few centimetres below the outlet and is not filled to the brim. Round up to the next size you can buy.
📐 The Formula
Daily Water Requirement Formula
The calculation starts from a planning value per adult for your comfort level, adds water for activity, raises or lowers the climate-sensitive uses, and counts each child as 65% of an adult:
Daily Total (L) = L_adult × (Adults + 0.65 × Children)
L_adult = Base × (1 + (Climate Factor − 1) × climate-sensitive share) + Activity × Climate Factor
Climate-sensitive share = bathing + drinking & cooking + garden (49% of the standard base)
Climate Factor: Temperate 1.0, Hot/Arid 1.4, Tropical 1.2, Cold 0.9
Recommended Tank (L) = Daily Total × Buffer Days × 1.15 (15% headspace)
Base Consumption by Comfort Level
Comfort Level
L/person/day
Basis
Typical Use Case
Minimum
50 L
WHO "intermediate access" level
Outages, water-scarce periods
Basic
80 L
Within the UN/WHO 50–100 L basic-needs range
Rural households, water-scarce areas
Standard
130 L
Planning value: piped home, efficient fittings
Typical family home, city supply
High Comfort
200 L
Planning value with garden (US average is about 310 L)
Garden, pool top-up, dishwasher, long showers
Activity Level Modifier
Physical activity increases drinking water and washing. This calculator adds a fixed amount per adult, split between drinking and bathing — planning values, not measured averages:
Activity Level
Extra L/person/day
Reason
Low (Sedentary)
0 L
Office work, minimal exertion
Moderate
+8 L
Light exercise, physical work
High
+20 L
Daily sport, outdoor labour
🚿 Where Your Water Goes
Daily Water Usage by Activity
Understanding how water is consumed in a household makes it easier to identify where savings are possible or where demand spikes during specific activities.
🚽
Toilet Flushing
Older toilets use about 9–26 L per flush depending on age. Modern dual-flush: about 4–6 L full, 2.6–4 L half; US WaterSense toilets use no more than 4.8 L (1.28 gal). Often a quarter or more of indoor use.
🚿
Bathing / Showering
About 50–95 L for an 8-minute shower — WaterSense showerheads use at most 7.6 L/min, standard US heads up to 9.5 L/min. A full bath uses roughly 80–150 L. Often the largest single indoor use.
🍽️
Cooking & Drinking
2–4 L for drinking, 5–15 L for cooking and food prep. The WHO drinking-water guidelines assume an adult drinks about 2 L a day; heat and hard work can double that.
🧺
Laundry
About 40–150 L per wash cycle: front-loaders roughly 40–60 L, older top-loaders up to 150 L. Spread across the week, often 20–40 L per person per day.
🌿
Garden / Outdoor
0–200+ L a day depending on garden size and season. A garden hose running 20 minutes can use 200–400 L. US EPA says outdoor use is over 30% of household use on average, and up to 60% in arid regions.
🪣
Cleaning
Hand-washing dishes: 6–18 L. Dishwasher: 9–15 L. Floor mopping and general cleaning: 10–30 L/day for a typical 3-bedroom home.
🏠 When to Use This
Common Use Cases for This Calculator
Sizing a Household Water Tank
Before buying a storage tank, you need to know your daily demand. Four adults at standard comfort and moderate activity in a hot climate need roughly 667 L/day, so a 3-day buffer tank should hold at least 2,300 litres including 15% headspace — in practice a 2,500 L tank. Use our Tank Size for Home Calculator for a full sizing walkthrough.
Planning for Water Supply Interruptions
If your municipal supply is unreliable or you're planning an off-grid setup, knowing daily requirements lets you plan storage accurately. A 7-day buffer at 500 L/day means 3,500 litres of water, or about 4,000 litres of tank once 15% headspace is added — for example two 2,000 L tanks connected together.
Emergency Preparedness
Ready.gov (FEMA) and the CDC recommend storing at least 1 gallon (3.8 L) per person per day for at least 3 days — for 4 people, about 45 litres, covering drinking and basic sanitation only. Keeping a home running normally takes far more: at the 50 L minimum level, 4 × 50 × 3 = 600 litres; at standard comfort, 4 × 138 × 3 ≈ 1,660 litres. Use our 72-Hour Water Supply Calculator for emergency-specific estimates.
Rainwater Harvesting System Design
Knowing your daily consumption tells you how much catchment area and tank volume you need for a viable rainwater system. If you need 400 L/day (about 12,000 L a month) and average 80 mm of rain a month on a 100 m² roof, the roof receives 8,000 L, and after typical losses (a runoff coefficient around 0.8) you collect roughly 6,400 L — only about half your demand, so you would need mains top-up or a bigger roof. See our Rainwater Harvesting Calculator.
🧮 Worked Example
Worked example: a family of four in a hot city
Two adults and two children live in a hot, dry city with moderate activity and a standard household. Mains water comes every other day with occasional longer gaps, so they want 3 days of storage.
Per adult: standard base 130 L. Bathing, drinking and garden use (49% of it, 63.7 L) rise by 40% in the heat: +25.5 L. Moderate activity adds 8 L × 1.4 = 11.2 L. Total ≈ 166.7 L per adult per day.
Tank: 550 × 3 days × 1.15 ≈ 1,898 L, so a 2,000 L tank is the right size.
The same family in a temperate climate needs about 455 L/day; a household of four adults there needs about 552 L/day.
❓ FAQ
Frequently Asked Questions
How much water does a person need per day?
For drinking alone, an adult needs about 2–3 litres a day, more in heat. For a household, the WHO links about 50 litres per person per day with low health risk and 100 litres or more with optimal access; the UN and WHO say 50–100 litres meets most basic needs. Actual use in piped homes ranges widely — US homes average about 310 litres (82 gallons) per person per day, including garden watering.
How much water does a family of 4 use per day?
With this calculator's standard settings (130 L base, moderate activity, temperate climate), four adults need about 550 litres per day. With two children instead of two adults, that drops to about 455 litres. In a hot climate with high activity, four adults could need about 730 litres per day.
What size water tank do I need for my household?
Multiply your daily requirement by the number of buffer days you want, then add 15% headspace. A family using 500 L/day wanting a 3-day buffer needs: 500 × 3 × 1.15 = 1,725 litres minimum. Round up to the nearest available size — typically 2,000 L in this case.
How does climate affect daily water requirements?
Heat mainly raises drinking, bathing and garden watering — Ready.gov notes drinking needs can double in very hot temperatures, and US EPA says outdoor use can reach 60% of household use in arid regions. Toilets, laundry and cleaning change little. That is why this calculator applies its climate factor (×1.4 hot, ×1.2 tropical, ×0.9 cold) only to those climate-sensitive uses, raising a standard household's total by about 20% in a hot climate.
What is the WHO minimum water requirement per person?
In emergencies, the Sphere humanitarian standards and WHO emergency guidance use about 15 litres per person per day as the minimum for drinking, cooking and basic hygiene. For everyday life, the WHO report Domestic Water Quantity, Service Level and Health describes about 20 litres as basic access (high health concern), about 50 litres as intermediate access (low concern) and 100 litres or more as optimal. This calculator's "Minimum" setting uses 50 L.
How many buffer days of storage should I plan for?
It depends on how reliable your supply is. Homes on a reliable mains supply often keep a day or two; where water comes on alternate days or outages are common, 3–7 days is a common choice. Homes that rely on deliveries or rainwater should plan for the longest gap they expect between refills. Emergency agencies separately advise keeping drinking water for at least 3 days, and 2 weeks if possible.
Does activity level really change water consumption significantly?
Somewhat — a physically active person may drink 1–2 litres more and shower more often than a sedentary one. This calculator adds 8 L (moderate) or 20 L (high) per adult; for four adults, high versus low activity adds 80 litres a day in a temperate climate and 112 litres in a hot one. Comfort level and garden use matter far more.
✅ Sources & Review
Sources and review
The comfort levels and the climate, activity and child factors are planning values; the benchmarks they are checked against come from these references:
US EPA WaterSense — Statistics and Facts: 82 gallons (about 310 L) per person per day at home; outdoor use over 30% on average, up to 60% in arid regions. Fixture limits from WaterSense showerheads.
Ready.gov (FEMA) — Water: at least 1 gallon per person per day for emergencies; needs can double in very hot temperatures.
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.
