1. Define the boundary
Decide which meter and equipment are included. Record whether landscaping, restrooms, make-up water, RO feed or another tenant shares the meter.
2. Record comparable readings
Capture start and end readings in the same unit. Confirm rollover, multiplier and decimal conventions before subtracting.
3. Match throughput
Use the actual vehicle count for exactly the meter interval. Separate test washes, maintenance cycles and unusually long rewash events where possible.
4. Describe operating conditions
Record wash type, active arches or options, reclaim status, RO status, weather, leaks, maintenance and known downtime.
5. Calculate per-vehicle use
Divide interval water by interval vehicles. Also calculate per-day use so a low-volume interval does not hide continuous leaks or cleaning demand.
6. Repeat the baseline
Use several comparable intervals and retain the individual results. Investigate changes rather than averaging unlike seasons, wash packages or equipment states.
7. Map each stream
Separate fresh process water, reclaimed water, spot-free permeate, RO reject, carryout/evaporation, backwash and discharge before proposing a retrofit.
8. Keep evidence
Retain meter photos or exports, vehicle counts, dates, equipment notes and calculation inputs so post-project performance can be compared fairly.
Worked example
An interval rises from 100,000 to 115,000 L while 300 vehicles are processed in five days. The baseline is 50 L/vehicle and 3,000 L/day; across 300 comparable operating days that projects to 900 m³/year.
Sources
- U.S. EPA WaterSense at Work — Vehicle Washes
- U.S. Department of Energy — Vehicle Wash Water-Use Estimating Methods
- International Carwash Association — Water Use, Evaporation and Carryout