Your water bill arrives, and it is higher than last month. Nobody changed anything, or so you think. Was it the garden? The new dishwasher? A tap that drips at night?
Calculating your water usage and cost is the first step to finding out. You can do it two ways: read it from your meter and bill, or estimate it from daily habits. This guide shows both, with simple examples.
Quick Answer
Water usage = Current meter reading − Previous meter reading
Water cost = Usage × Rate per unit + Fixed charges
For example, if your meter shows 250 cubic feet of use in a month and your total rate is $10 per 100 cubic feet, the usage cost is $25, plus any fixed charges on your bill.
Know Your Units First
Water companies measure water in different units, so check your bill.
| Unit | What it means |
|---|---|
| Gallon | A US gallon is about 3.785 litres |
| Cubic foot (cu ft) | 1 cubic foot = about 7.48 gallons |
| CCF (or HCF) | 100 cubic feet = about 748 gallons |
| Cubic metre (m³) | 1 m³ = 1,000 litres (about 264 US gallons) |
| Litre | Common for small amounts |
Method 1: Calculate From Your Water Meter
- Find your meter. It is usually outside near the street or in a basement or utility area.
- Write down the reading. Note the date and time.
- Read it again later. For example, a month later, or at the same time on your bill cycle.
- Subtract. Current reading − previous reading = water used.
- Convert the units if needed.
Example:
- Previous reading: 12,450 cu ft
- Current reading: 12,700 cu ft
- Usage: 250 cu ft = 2.5 CCF = about 1,870 gallons
How to Calculate Your Water Bill
Bills often have more than one line. The rates below are made up for illustration, so please use the ones on your own bill.
| Charge | Calculation | Cost |
|---|---|---|
| Water usage | 2.5 CCF × $4.50 | $11.25 |
| Sewer charge | 2.5 CCF × $5.50 | $13.75 |
| Fixed service fee | Per bill | $20.00 |
| Total | $45.00 |
Check your bill for these common features:
- Fixed (service) charges that you pay no matter how much you use.
- Sewer or wastewater charges, often based on your water use.
- Tiered or block rates, where the price per unit rises as you use more.
- Seasonal rates, which can be higher in summer.
- Taxes and other fees.
Method 2: Estimate From Daily Habits
No meter handy, or want to know where the water goes? Estimate it. The numbers below are typical, but your fixtures may use more or less.
| Activity | Typical use |
|---|---|
| Shower | about 2 to 2.5 gallons per minute |
| Toilet flush | about 1.3 to 1.6 gallons (older toilets use more) |
| Dishwasher | about 4 to 6 gallons per load |
| Washing machine | about 15 to 30 gallons per load |
| Running a tap | about 1.5 to 2 gallons per minute |
Example for a household of 4 (per day):
- Showers: 4 people × 8 minutes × 2 gallons per minute = 64 gallons
- Toilets: 4 people × 5 flushes × 1.6 gallons = 32 gallons
- Laundry: 1 load × 20 gallons = 20 gallons
- Dishwasher: 1 load × 5 gallons = 5 gallons
- Kitchen and hand washing: about 20 gallons
- Total: about 141 gallons a day
Over 30 days, that is 141 × 30 = 4,230 gallons, or about 5.65 CCF. At an illustrative combined water and sewer rate of $10 per CCF, usage costs about $56.50, plus a $20 fixed fee for a total of roughly $76.50.
Your real bill may be higher than an estimate like this, because it can include outdoor watering, leaks and extra use.
How Much Does a Single Activity Cost?
At the example rate of $10 per CCF (about $13.37 per 1,000 gallons):
- An 8-minute shower at 2 gallons per minute uses 16 gallons and costs about $0.21 in water.
- A 10-minute shower at 2.5 gallons per minute uses 25 gallons and costs about $0.33.
For hot water, heating adds an energy cost on top, which can be larger than the water cost itself.
How to Check for Leaks
A hidden leak can quietly raise your bill.
- Turn off all taps and appliances.
- Look at your meter. If the dial or low-flow indicator moves, you may have a leak.
- Test the toilet. Add a few drops of food colouring to the tank. If colour appears in the bowl within 15 minutes without flushing, the flapper may be leaking.
- Check taps, pipes and outdoor hoses for drips or damp spots.
Even small leaks can waste thousands of gallons a year.
Easy Ways to Lower Your Water Bill
- Fix leaks and dripping taps quickly.
- Install low-flow showerheads and tap aerators.
- Run dishwashers and washing machines only with full loads.
- Shorten showers by a minute or two.
- Water the garden early in the morning or evening, and only when needed.
- Replace very old toilets with water-efficient models, if suitable.
Common Mistakes to Avoid
- Mixing units, such as cubic feet on the meter with gallons in your estimate.
- Ignoring fixed fees and sewer charges when working out cost.
- Forgetting tiered pricing, which changes your cost per unit.
- Using other people’s rates. Water prices vary a lot by area.
- Not checking for leaks before blaming usage.
Frequently Asked Questions
How do I calculate water usage? Subtract your previous meter reading from the current one, then convert to gallons, litres or cubic metres.
How much water does the average person use per day? It varies widely by country and lifestyle. In the US, estimates from environmental agencies are often around 80 to 100 gallons per person per day at home.
How many gallons are in a CCF? One CCF is 100 cubic feet, which is about 748 gallons.
How do I calculate my water cost per month? Multiply your monthly usage by the rate per unit on your bill, then add sewer charges and fixed fees.
Why is my water bill so high? Common reasons include leaks, seasonal watering, higher rates, more people at home, or an estimated meter reading. Check your meter and your bill.
Final Thoughts
To calculate water usage and cost, read your meter, subtract the previous reading, convert to the units on your bill, and multiply by the rates. Estimating from daily habits can show where the water goes. Check for leaks often, and compare your numbers month to month.
Disclaimer: This article is for general information only. Water rates, units and fees vary by provider and location, and example numbers are illustrative. Please check your own bill or contact your water utility.