Integrating approach to maintaining quality
Bob Borrill, water supply process manager at West Midlands Region of Severn Trent Water, explains how the collection and interpretation of data, often provided by computer control systems, is vital in the drive to improve the standard of service provided to its customers.
Severn Trent Water has recognised for some time that Œacting on facts’ via
the collection and interpretation of relevant data is vital in the drive to
continually improve the standard of service provided to its customers.
In addition to controlling processes, the MWCS gather data from a suite of
continuous, on-line water quality monitors, monitoring concentrations or
values of parameters such as chlorine, turbidity, pH and coagulant residual
at various stages through the treatment process.
Data from these monitors is collected and displayed in real time as trends,
allowing the works operator to detect and correct deviations from normal
It isn¹t enough however just to collect the data. Should an adverse trend
start to appear in any particular data set it is vital that the operator
responds quickly with corrective action. This is achieved in Severn Trent by
the use of discrete data collection, data verification and data
interpretation stages as follows:
– collection continuous, on-line water quality monitors feed data to the
– verification on site analytical tests verify monitor accuracy; and
– interpretation procedures provide advice to operators should adverse
data trends start to develop.
Ultimately Severn Trent Water’s performance with respect to drinking water
quality is determined by analytical results from statutory samples analysed
at Severn Trent Laboratories, an accredited laboratory using sophisticated
analytical techniques. This data however is not immediately available to the
water treatment plant operator who needs real-time data from water quality
monitors and on-site tests to optimise treatment processes.
In order to standardise on-site water quality monitoring across the company
Severn Trent Water has developed an ŒOn-Site Water Quality Testing manual’
which provides a standardised approach to real-time water quality monitoring
within a flexible framework.
The primary objectives of the manual are to ensure that appropriate
parameters are monitored at the correct frequency using established best
practice for sampling, analysis and record keeping.
Water quality data is derived from a mixture of continuous on-line monitors
and on-site tests and the On-Site Water Quality Testing manual provides
standard instructions on the way in which the two monitoring methods should
Water quality parameters are separated into two categories; ŒRegion 1′ and
– Region 1 parameters are the core testing suite which are critical to
process plant control and performance. These parameters are usually
monitored continuously. Should a continuous monitor fail for any reason the
frequency of on-site tests is increased to compensate until the monitor is
repaired. The manual prescribes the minimum testing frequency to be used.
– Region 2 parameters such as conductivity, manganese and ammonia are viewed
as additional core tests appropriate to the treatment process in question
and they are more usually measured by on-site tests rather than continuous
monitors. A procedure for determining the testing frequency of Region 2
parameters is included in the On-Site Water Quality Testing manual. The
procedure assigns scores to elements such as Œcriticality’, Œspeed of
impact’ and Œwhether the monitor controls dosing of a chemical’ in order to
determine the frequency of on-site testing.
The manual covers the whole range of tests required to operate a modern
water treatment plant effectively including tests to ensure that treated
water has an acceptable taste and odour and tests on waterworks sludge to
check sludge treatment plant efficiency.
Continuous on-line monitors are maintained and calibrated within a
pre-planned maintenance programme but it is prudent to check monitor
accuracy regularly in between maintenance visits by checking the monitor
against a simple on-site analytical test.
Severn Trent Water’s water quality procedures play a vital part in the
management of water treatment processes. Their power lies in the way in
which they encapsulate the knowledge and experience gained at a water
treatment works over many years to help operators provide an instant,
informed response to problems 24 hrs/day. The procedures start by stating
the alarm level for the parameter in question after which operators are
prompted to read a short section containing important data such as who needs
to be informed and how time critical the problem is.
The main body of the procedure contains sections on checks to be carried out
and possible remedies and this is where historical expert knowledge of the
plant is encapsulated.
Severn Trent Water now has a standardised approach to on-site water quality
testing at its water treatment works thanks to sophisticated data collection
and trending systems coupled with the standardised approach provided by the
codified On-Site Water Quality Testing manual. Feeding this data into water
quality procedures provides advice 24 hours a day through encapsulated
expert knowledge, which helps to ensure that Severn Trent’s customers
continue to receive very high quality drinking water.