Audit Methodology

Chapter 3: Water Balance

3.1 Introduction

A flowmeter reading program and subsequent water balance calculation ensure that all water uses in a facility are identified and adequately quantified. If available, historical monthly and yearly average daily flows, along with schematic diagrams of the domestic hot/cold water systems, should be assembled to determine the relationship between the flowmetering period and annual variations. Other actions, such as plotting flowmeter readings and making an inventory of fixtures, further contribute to a speedy audit process. Because of the short time frame of most audits, it is necessary to establish a program of manual meter reading by the staff on site at each facility.

The next step in water balance calculation uses the information gathered from site inspections, measurements, and discussions with site operators and users. An opportunity should be taken to provide more than just a volumetric total in the balance. For example, each individual water use may be placed in its appropriate category: domestic, cooling, process, outdoor, or fire. The location and period of use during the day are to be shown, along with the method of discharge to the storm or sanitary sewer. An analysis is then completed of the average daily, peak, and base flow for each facility.

If the results show that the sum of water used in all operations is less than the total water supplied, it is assumed that water uses exist that have not been included in the balance, or that either the main meter or its reading is inaccurate. The water balance should be re-examined until the auditor is satisfied that all operations have been considered.

Distribution system water losses (leaks) are normally considered as part of the water balance. However, since the distribution system pipes are visible in the facility's buildings, water leaks would be noticed and repaired without delay, so such losses may not necessarily be considered.

3.2 Water meter reading program

The water meter reading approach was successfully employed for the pilot audits, because it provided the level of data required for a water audit. Readings are usually taken at least twice a day, in the morning before the main daytime activity begins and late in the afternoon at the end of the normal working day. For a continuous period of several weeks, including weekends at most sites, the daily readings were recorded. In this manner the daytime and nighttime base flows were established. It should be noted that more frequent readings were taken at many pilot audit sites for greater accuracy.

The alternative method of obtaining flow data from the existing and newly installed flow meters would have been to use data loggers with recording heads attached to the meters. With this technique one can gather data much more frequently, by recording the flows at short time intervals. In most cases, however, the cost to hire or purchase the equipment, set up, check weekly, and remove meters at a large number of locations would be far greater than that of the manual method chosen.

It is advantageous to use standardized forms for meter reading purposes before the audit. An example sheet is presented in Appendix A. Upon completion, these should be forwarded to an established location for safekeeping.

In the absence of earlier records, several months lead time in flowmeter readings may reduce the costs of the audit.

3.3 Facility-wide water balance

The objective of the facilitywide water balance is to add up all of the individual categorized water use volumes and equate them to the volume of water supplied to the facility as recorded by the main meter. The first step in preparing the water balance is to examine the facility as a whole. It might also be advantageous to divide the complex into smaller, individually metered water-using sub-areas.

The smaller sub-areas are chosen to represent a logical area of water use, while respecting geographical boundaries. When buildings are located beside each other, but have separate meters and different management, they should be divided for the purposes of the water balance.

The water balance for the entire facility can be presented in figures showing meters and sub-areas, and in tables showing a comparision between individual water uses by incoming water volume to the total volume of water used in each sub-area.

3.4 Main meter water balance

The methodology for conducting a main meter water balance is to equate the total water volume supplied to the facility with the total water volume supplied to each sub-area of the facility. Results from the main meter water balance are most easily presented in flow chart form.

The main meter water balance considers only the total water supplied to the facility and the total water volume supplied to each sub-area. It aims to

• identify sub-areas of major water use
• identify major discrepancies between the main water volume supplied to the facility and the sum of water volumes supplied to each sub-area
• highlight sections of concern around which an individual water balance can subsequently be carried out

Depending on the magnitude of unknown flow values, a decision will be made whether to

• consider the mass balance complete
• install new flow meters to monitor areas of concern
• use water use estimations for the sub- areas within the unmetered areas to estimate the total water supplied

3.5 Sub-area water balances

The primary objectives of the sub-area water balances are to identify the volumes of water used by each operation in the area and to sum these to account for the total volume of water used in the area. This information may be shown as flow diagrams for the water balance in each sub-area.

3.6 Summary

The completion of facility water balances, in which all major water uses are accounted for (within a reasonable margin of error) concludes the water audit part of the process. The water audit results are then used in the next phase for designing a water efficiency program specific to the facility under study.

Table of Contents  Previous  Next