Calculator Inputs
Example Data Table
| Scenario | Baseline (L/day) | Improved (L/day) | Units | Reuse % | Leak % | Days |
|---|---|---|---|---|---|---|
| Office block retrofit | 1,000 | 720 | 12 | 0 | 3 | 365 |
| Residential efficient fixtures | 1,250 | 850 | 24 | 5 | 2 | 365 |
| Site welfare facilities upgrade | 650 | 460 | 8 | 0 | 6 | 300 |
| Rainwater-assisted washdown | 900 | 700 | 6 | 15 | 1 | 250 |
Formula Used
1) Annual baseline demand (L): Baseline L/day × Units × Days
2) Annual improved demand (L): Improved L/day × Units × Days
3) Raw savings (L): max(0, Baseline annual − Improved annual)
4) Reuse savings (L): Improved annual × (Reuse% ÷ 100)
5) Leak savings (L): Baseline annual × (Leak% ÷ 100)
6) Total savings (L): min(Baseline annual, Raw + Reuse + Leak)
7) Cost savings: based on either m³ or 1,000 gallons pricing.
8) CO₂ avoided (kg): Saved m³ × CO₂ factor (kg/m³)
How to Use This Calculator
- Enter baseline daily water use per unit.
- Enter the improved daily use after upgrades.
- Set the number of units and operating days.
- Add reuse and leak reduction percentages if relevant.
- Choose your billing unit and input your price.
- Optional: add upfront cost for payback estimate.
- Press Calculate Savings to view results.
- Use the CSV or PDF buttons for reporting.
Practical Notes for Construction Water Savings
Baseline profiling and data quality
Start with metered or logged daily consumption where possible. If only weekly or monthly totals exist, normalize to liters per unit per day to compare across buildings, welfare blocks, or temporary site zones. Typical mixed-use site operations often range from 400–1,500 L/unit/day depending on occupancy, cleaning, and washdown activities. Use at least 14 days of representative data to avoid abnormal weather and commissioning periods.
Efficiency upgrades and realistic improvement targets
Efficient fixtures, timed taps, low-flow showerheads, and controlled hose connections can reduce demand by 15–40% in many projects. For welfare facilities, a reduction of 200–500 L/unit/day is common when replacing older fittings and adding flow restrictors. Pair hardware changes with simple controls, such as automatic shutoff valves, to protect savings during high-traffic shifts.
Reuse and recapture planning
Reuse percentage represents demand offset by rainwater, greywater, or process recovery. Practical offsets are often 3–15% without major storage, and 15–35% where dedicated tanks and treatment are installed. Apply reuse only to the improved demand, because recaptured water typically substitutes part of ongoing usage rather than changing baseline behavior.
Leak reduction and operational controls
Leakage reduction captures savings from pressure management, rapid repair response, and sub-metering alarms. Even a 1–5% leak reduction can be material on large sites. Regular night-flow checks, weekly inspection of hose reels, and automatic isolation for unused zones reduce hidden losses while improving safety and hygiene.
Reporting outcomes and payback
Annual cost savings depend on your tariff unit: per m³ or per 1,000 gallons. Combine financial savings with avoided CO₂ using a local kg/m³ factor to support sustainability reporting. For capital upgrades, payback is the upfront cost divided by annual savings; projects often target payback under 2–4 years for approvals.
FAQs
1) What does “unit” mean in this calculator?
A unit is any repeatable group you track: apartments, rooms, welfare blocks, work zones, or equipment bays. Pick one definition and keep it consistent between baseline and improved inputs.
2) How should I estimate baseline liters per day?
Use meter readings where possible. If you have monthly consumption, divide total liters by operating days, then divide by the number of units. Avoid including one-off events like hydrotesting.
3) Why is reuse applied to improved demand?
Reuse usually substitutes part of ongoing consumption after efficiency actions are in place. Applying reuse to improved demand prevents double counting savings already captured by lower fixture flow rates.
4) What leakage reduction percentage is reasonable?
Many sites start with 1–3% as a conservative assumption. With sub-metering, night-flow checks, and fast repairs, 3–8% can be achievable, especially on large temporary networks.
5) Can I use this for short projects?
Yes. Set “days per year” to your project duration in days. The calculator will scale water, cost, and CO₂ savings to that timeframe for more accurate budgeting.
6) The currency symbol is different from mine. How do I change it?
Edit the currency symbol in the code where annual cost savings is formatted. The calculation uses your tariff value; only the display symbol is cosmetic.