Audit Methodology

Chapter 2: Inventory of Water Use Operations

2.1 Introduction

The primary reason for describing the water uses for each point of extraction is to develop a comprehensive inventory of water uses at the facility and to identify potential water reduction strategies.

To obtain such information, one might

• contact area personnel and arrange for meetings
• survey area personnel about the water uses in their area
• transfer information from questionnaires to spreadsheets and floor plans
• verify information with plumbing drawings and building personnel

The information regarding water use operations might be obtained through the use of aspecifically designed questionnaire (e.g., Appendix A).

With all system components defined and located, the water uses for all of the points of extraction are described, including

• category of water use
• volume, rate, and frequency of use
• water lost or consumed

There are some situations in which further investigation of flow quantity for a water use is not warranted, for example:

• uses that occur rarely (e.g., fire hoses)
• uses that are very small compared to the total facility use
• uses that will not affect the water balance (e.g., non-city water)

The results of a water use survey are best summarized in computer-generated table forms for effortless retrieval and review.

2.2 Procedures for estimating flows

Past experience suggests that although during the audit, descriptions of water uses are readily attainable, in most areas volumes of water used are not measured. If a flow estimate is needed, published values or field measurements may be acceptable.

Tabulated values from published information are available for most conventional water uses to estimate flow use by specific operations. These may be augmented by estimates regarding the number of users per day or duration of use.

Estimation of flows might be based on field measurements, which may be more appropriate for some water use operations. Methods of field measurement include

• flow meters on either the water distribution system or the water-using equipment (e.g., cooling water pipe)
• bucket and stopwatch measurement of water extracted for a specific operation
• volume/frequency measurement of water used for a specific operation

Indirect methods of flow measurement (such as logging the operation of water pumps, and displacement tests on water storage tanks) are likely to produce lower quality data.

It is important to measure flows over the same general time period, because the periodicity and seasonality of flows may affect the water balance equation. Part of the margin of error at a pilot site was due to unknown flows for irrigation and lawn watering. If outdoor use is suspected, the water audit should be carried out during the summer season.

However, any other method for measuring flow that appears to be reasonable for the application may be used.

2.2.1 Flow meters

An essential element of any water audit is the measurement of the main flow entering the facility. Additional flow measurement into sub-areas is occasionally warranted when significant portions of the total flow need to be ascertained.

Flows can be measured by either permanent flow meters, which give the most reliable results both during the investigation and after the water audit is finished, or temporary recorders, typically situated at a specific location for the short audit period. Temporary flow meters, if not installed correctly, may give corrupt results.

Permanent flow meters are costly and have to be fitted into the pipe run. However, they will give highly accurate daily, weekly, monthly, seasonal, and unusual-event data during the water audit, and then continue to give long-term results and trends.

There are two basic types of temporary flow meters, namely, external clamp-on devices and insertion flow recorders.

External clamp-on meters send ultrasonic signals through the pipe wall and across the water flow. They are useful where only an indication of the flow range is required and they need no pipework modifications. However, they require a straight section of pipe at least 30 diameters in length for installation.

The insertion flow meter requires a point of entry into the main via a small (5 cm or 2 inch diameter) tapping. An electromagnetic head, or a small turbine, measures the velocity of flow at one point in the pipe. The pipe has to be traversed to obtain a flow profile, from which the relationship between measured point velocity and total flow can be calculated.

Varying flow profiles and internal pipe corrosion can cause distortions. Results from insertion meters are likely to be more accurate than those from clamp-on meters.

2.2.2 Bucket and stopwatch estimation

If the flow is constant and free flowing, as in some cooling waters, a bucket and stop watch approach can be used to estimate flow. The time it takes a bucket of a known volume to be filled by the free-flowing source is measured and a flow can be calculated.

2.2.3 Volume/frequency estimation

If the flow is not free flowing but fills a known volume, the frequency with which the volume (tank) is emptied or replaced can be used to estimate flow.

Occasionally, logging the operation of a domestic cold water pump is the last resort to obtain a set of (indirect) flow measurement. The method produces lower quality of data but gives an understanding of the water using pattern at a facility and also provides information on the operation and control of the pumped system.

2.3 Leakage detection surveys

Significant lengths of outside underground mains are potential areas for leakage of water. Such conditions may warrant the consideration of a leakage survey.

The leak detection technique involves using an electronic leak correlator and a noise sounder. The leakage of water from a pipe produces unique noises, which the electronic equipment is able to detect. Sensing devices are usually attached to the watermain fittings, such as hydrants and valves, and the survey is completed in a methodical manner around the site. If the results are "quiet," there is no leakage.

Table of Contents  Previous  Next