🏠 About This Category
What Are Household Sizing & Water Requirement Calculators?
Household water planning is rarely guesswork-friendly. Too small a tank and you run dry during supply interruptions; too large and you're paying for unused capacity while stagnant water creates health risks. The six calculators in this category take the uncertainty out of every decision — from finding your family's daily litre count to sizing a shared tank for a multi-story apartment block or a school campus.
These tools are designed for homeowners, building managers, property developers, water engineers, and anyone else who needs to answer the question: how much water do I need, and for how long? All calculators follow WHO minimum standards and ASHRAE commercial benchmarks, and results can be adjusted for regional norms, climate conditions, and different usage profiles.
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WHO Minimum
50 litres per person per day covers basic drinking, cooking, and sanitation needs.
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Comfort Standard
100–200 L/person/day for full domestic comfort including laundry and garden use.
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Commercial Use
Office buildings typically need 40–60 L per employee per day for washrooms and kitchens.
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Buffer Days
Most authorities recommend 2–3 days of stored autonomy as a minimum safety margin.
🔍 How to Choose
How to Choose the Right Calculator
Start with daily usage, then work to tank size. The Daily Water Requirement Calculator should always be your first stop — it gives you the baseline consumption figure that every other calculator in this category depends on. Until you know your daily demand in litres, tank-size estimates are just guesses.
Sizing a tank for an existing home? Use the Water Tank Size for Home Calculator. It takes your daily figure and lets you dial in a refill interval (how often the mains or tanker refills your tank) to produce a recommended minimum capacity. Increase the buffer days if your area experiences frequent outages.
Trying to manage an existing supply? The How Long Will My Tank Last Calculator is your tool. Feed it your current fill volume and daily consumption, and it tells you exactly when you'll run out — useful for scheduling deliveries or managing usage during droughts.
Multi-unit residential or apartment buildings should use the Apartment Tank Size Calculator, which aggregates demand across units and can account for variance in occupancy. For offices, retail premises, hotels, or restaurants, the Commercial Water Tank Size Calculator applies industry-standard per-head consumption rates for different building types.
Schools, hospitals, mosques, and community buildings have highly variable demand — dense in operational hours, near-zero outside them. The School & Institutional Calculator is built for this profile, letting you input daily population and facility type to produce a storage recommendation that accounts for peak usage windows.
| Your Situation | Best Calculator | Key Inputs |
|---|
| Family home, unknown usage | Daily Water Requirement | People, lifestyle |
| New tank purchase for home | Tank Size for Home | Daily use, refill interval |
| Managing existing supply | How Long Will It Last? | Current volume, usage/day |
| Apartment / multi-unit block | Apartment Tank Size | Units, avg. occupancy |
| Office / hotel / restaurant | Commercial Tank Size | Staff count, property type |
| School / hospital / mosque | School & Institutional | Daily visitors, facility type |
Tip: Always add a 15–20% safety buffer on top of the calculated tank size. Water demand spikes unpredictably — guests, garden irrigation during dry spells, and leaks all increase consumption beyond your baseline estimate.
❓ FAQ
Frequently Asked Questions
How much water does a household of 4 need per day?
The WHO minimum is 50 litres per person per day for basic needs — drinking, cooking, and sanitation. Most households in developed regions use 100–200 litres per person daily. A family of 4 typically needs 400–800 litres per day depending on lifestyle, climate, and appliance use. Use the Daily Water Requirement Calculator for a figure tailored to your household.
What size water tank do I need for my home?
Tank size depends on daily consumption, how often your tank gets refilled, and how many buffer days you want. A common starting point is storing 2–3 days of household supply. For a family of 4 using 500 L/day, that means a 1,000–1,500 L tank. For areas with unreliable supply, sizing for 5–7 days is wiser. Use the Water Tank Size for Home Calculator to get a precise recommendation.
How do I calculate how long my water tank will last?
Divide the tank's current water volume (in litres) by your daily consumption. A 1,000 L tank used at 250 L/day lasts 4 days. If the tank is only 60% full, that's 600 L ÷ 250 L/day = 2.4 days. Use the How Long Will My Tank Last Calculator to get this instantly without the arithmetic.
Is a rooftop tank or underground tank better for a home?
Rooftop tanks deliver water by gravity — no pump needed — but they add structural load to your building and water can heat up in exposed tanks. Underground tanks stay cool (better for water quality and taste), have no height restrictions, and keep rooftops clear, but require a pump and are harder to inspect. The right choice depends on your building structure, budget, and pressure requirements. A structural engineer should assess rooftop installations for any tank over 500 L.
How much water does an apartment building need?
Multiply the number of residents by per-capita daily usage (typically 150–200 L/person for urban apartments), then factor in your autonomy target. A 10-unit building with 2 residents each at 160 L/day needs 3,200 L for one day, or 9,600 L for three days. Use the Apartment Water Tank Size Calculator to account for unit variance and peak demand times.
What daily water allowance should I use for planning?
Use 80–100 L/person/day for conservative planning (basic domestic use: drinking, cooking, sanitation). Use 150–200 L/person/day for full comfort, including laundry, dishwasher, and garden. Commercial buildings vary: offices average 40–60 L/person, restaurants 30–50 L per cover, and hospitals 200–400 L per bed per day. The Daily Water Requirement Calculator provides recommended figures by usage profile.