Who should oversee hardness and TDS testing in a commercial water system?

Oversight should be assigned through a documented division of responsibility rather than left to the person who happens to collect the sample. The duty holder or responsible person should control the governance of the water system, while a technically competent water hygiene professional should define the testing approach, assess the significance of the results and advise on any necessary response. Where analysis is outsourced, the laboratory must use suitable methods and provide results in a form that can be understood and acted upon by the site team.

The duty holder’s role is to ensure that hardness and total dissolved solids (TDS) testing forms part of the wider water management arrangements. This includes confirming which systems require testing, approving the sampling plan, allocating responsibilities and ensuring that sufficient resources are available for investigation or remedial work. The duty holder does not necessarily need to carry out the technical assessment personally, but should be able to demonstrate that the process is controlled and that recommendations are not ignored.

The responsible person or site water manager usually coordinates the practical arrangements. They may maintain the asset register, identify relevant outlets and treatment equipment, provide access to plant rooms and review whether sampling has taken place as scheduled. They should also ensure that changes to the system—such as alterations to the incoming supply, water softener settings, heating equipment or distribution pipework—are communicated to the person providing technical advice.

A competent water hygiene professional should determine what the results mean in the context of the particular installation. Competence involves more than knowing how to use a test instrument. The assessor should understand the source water, treatment processes, operating conditions, materials, equipment manufacturers’ requirements and the intended use of the water. This is important because the same hardness or TDS reading can have different implications for a softened system, a process-water installation, a closed circuit or a building supplied by a private water source.

Hardness testing is commonly used to assess calcium and magnesium content, including whether a softener is performing as intended and whether scale formation may be likely. TDS provides an indication of the total concentration of dissolved substances, but it does not identify each substance individually. A TDS result should therefore not be treated as proof that water is wholesome, nor should it replace targeted chemical or microbiological testing where those tests are required. The person interpreting the result must understand the limits of each measurement.

The testing laboratory or sampling technician has a more specific role. The sampler should use clean, suitable equipment, follow the agreed sampling procedure and record the point, date, conditions and any relevant treatment status. If a sample is taken after a softener, for example, the result should be clearly distinguished from a sample taken before treatment. A laboratory report should identify the method used, the units, any reporting limitations and whether the result is outside the agreed control range.

Responsibility should also be clear where a specialist contractor undertakes the work. The contractor can provide technical findings and recommendations, but the client’s duty holder remains responsible for deciding how those recommendations are incorporated into the site’s water safety arrangements. A written scope should state:

• which systems, outlets or treatment stages are included;
• whether samples are taken before or after treatment;
• the test methods and reporting units to be used;
• the control limits or operational targets against which results will be reviewed;
• who receives the report and who authorises follow-up action; and
• how abnormal or unreliable results will be escalated.

Results should be reviewed alongside operating information rather than in isolation. A change in hardness may indicate a problem with softener regeneration, resin condition, bypass operation or the source supply. A change in TDS may warrant investigation of treatment performance, contamination, chemical dosing or a change in the water entering the premises. These possibilities cannot be confirmed from a single number, so the reviewer should compare the result with previous records and relevant system changes before selecting a remedy.

Where a result is unexpected, the competent adviser may recommend checking the sampling method, repeating the sample, testing an upstream and downstream point or examining the treatment equipment. Any repeat test should have a stated reason; repeating samples without investigating the cause can conceal a developing problem. If the finding could affect water safety, equipment operation or a control measure, the issue should be escalated through the site’s existing water management procedure.

The person overseeing the programme should be sufficiently independent to report an unfavourable result without pressure to dismiss it. They should also have access to maintenance records, treatment settings, previous test reports and relevant risk assessments. This information allows trends to be identified and helps distinguish a genuine change in water quality from a sampling or recording error.

For a commercial premises, the most reliable arrangement is therefore a named duty holder supported by a competent technical adviser, with laboratory or sampling responsibilities separately defined. The arrangement should be reviewed when the building use, water source, treatment equipment or distribution system changes. Clear role allocation ensures that hardness and TDS testing contributes to informed water system management rather than becoming an isolated laboratory exercise.