A household runs on two bills that behave very differently: water and electricity. The water demand calculator estimates how much water a household uses from people, fixture events, and other measured use. The home energy efficiency calculator compares billed annual electricity use against an alternative scenario you enter. Both are directional household resource tools, and both are deliberately modest: they add up what you enter, rather than scoring your home or promising savings.
The genuine choice is which resource you are examining. For the water side — daily gallons, annual gallons, and cost at your bill rate — the water page is the tool. For electricity intensity per square foot and how an alternative scenario compares with your billed use, the energy page is the tool. The two calculators share a design philosophy: scenario values in, transparent arithmetic out, with no hidden efficiency claim.
What each calculator does
The water demand calculator computes daily gallons as people × events per person-day × gallons per event, plus any other measured gallons per day; annual gallons multiply that total by 365, and cost applies the entered rate per 1,000 gallons. In its worked example, two people with 5 events per day at 1.6 gallons per event produce 16.0 gallons per day and 5,840 gallons per year. Every empirical factor is a scenario value you supply, with its measurement basis shown beside the inputs, and the page makes no climate, efficiency, WaterSense, or savings claim.
The home energy efficiency calculator computes each intensity as annual kWh divided by conditioned floor area in square feet, then reports the arithmetic difference between the billed and scenario values: (billed kWh − scenario kWh) ÷ billed kWh × 100. Its worked example: 12,000 kWh over 1,500 ft² is 8.00 kWh/ft²-year; a 10,000 kWh alternative scenario is 6.67 kWh/ft²-year, a 16.7% difference; equal scenarios give exactly 0.0%. The result is not an ENERGY STAR score, audit, forecast, or promised saving.
Side-by-side comparison
| Water demand calculator | Home energy efficiency calculator | |
|---|---|---|
| Resource measured | Household water use | Household electricity use |
| Primary inputs | People, events per person-day, gallons per event, other gallons, bill rate | Annual kWh, conditioned square feet, alternative scenario kWh |
| Core formula | Daily = people × events × gallons/event + other; annual = daily × 365 | Intensity = kWh ÷ ft²; difference = (billed − scenario) ÷ billed × 100 |
| Key outputs | Daily and annual gallons; annual cost at rate | kWh/ft²-year for both scenarios; percentage difference |
| Savings claim? | None — no WaterSense or efficiency claim | None — not a score, diagnosis, or promised saving |
| Use case | Water bill and fixture planning | Electricity benchmarking and scenario comparison |
When to use which
Use the water demand calculator when you are working with fixture labels, event frequencies, or a water bill: estimating what daily and annual use look like, or what a rate change means in dollars. Enter measured or label values, treat scenario ranges as sensitivity ranges rather than confidence intervals, and remember the page totals user inputs — it does not evaluate efficiency.
Use the home energy efficiency calculator when you have billed kWh and a conditioned floor area and want an intensity you can compare with an alternative scenario, such as a lighting swap or another usage level. The percentage difference is arithmetic, not a promise: it describes the gap between two entered scenarios. For real efficiency work, pair either tool with ENERGY STAR, DOE, and local utility guidance.
Where to start
- Water demand calculator — daily and annual household water use from fixture, event, and other measured inputs.
- Home energy efficiency calculator — annual electricity intensity and scenario comparison from billed kWh and floor area.
Informational note: This page is an educational comparison, not an efficiency audit, certification, or savings guarantee. Both calculators only total or compare user-entered scenario values, and neither establishes code compliance, forecast accuracy, or model validity. Verify any factor’s version, geography, and system boundary before relying on a result.