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  • James Howey

Water quality data - what to do?

“You can have data without information, but you cannot have information without data.” – Daniel Keys Moran

We need data to check that our treatment processes are working as required (e.g. critical control points) and verify that we are providing safe quality water to our customers.

However, we should not use data for only a check against numerical targets or guideline values. We should also do a systematic review and analysis of water quality data over an extended period, typically the preceding 12 months or longer.

This will help us identify emerging problems and trends and assist in determining priorities for improving drinking water quality.

Often statistical analysis of data is undertaken and presented in tables (e.g. minimum, maximum, mean, percentiles, exceptions etc). Other tools to enhance the interpretation of data should also be considered.

Visualisation is critical to data analysis. As is said, a picture is worth a thousand words! While tables are necessary to record the data, it is usually very difficult to distinguish pattern in tables of numbers, particularly for large data sets. Graphs, however, allow the reader to see complex data sets simply and concisely. Plots can reveal hidden structure in the data, and outlying or unusual results, and they enable preconceived ideas to be challenged (ADWG 2011).

But first of all, ensure that the data is recorded electronically, in a format that can make it easy to chart trends and interrogate data. Often data is recorded electronically, but in such away that it's difficult to interrogate. The best approach is to keep it in one table with fields in the columns and enter the records in the rows. A basic example is shown below, which is good for ease of entering data and reviewing it manually.

You can add features such as conditional formatting to flag results that are erroneous (in the wrong column) or are excursions.

However, if you want to get more sophisticated and use statistical software then the data needs to be saved slightly differently, as shown below.

If it is not possible to enter the data straight away at least have a system where data from hard copy log sheets is transcribed regularly into an electronic spreadsheet. It is always a struggle if it's left to the end of the year reporting period!

A good analysis of data is needed to undertake an effective review of your water quality risk management plan (e.g. DWQMP or DWMS or RWMP).

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