Water treatment

Safety first in hot water

A water heater full of scale

Hot water is one of the daily necessities we often take for granted unless the supply is interrupted, and it becomes a major inconvenience. But it is not only a matter of providing hot water reliably but also safely for the consumer. Andrew Dabin, product manager for Hamworthy Heating asks what are the risks involved for equipment and people, and what can be done to overcome them

treatment and maintenance schedule and whether the system is at a higher risk of breakdown due to site specifics such as hard water. In combination with this, an assessment of system design (e.g. to avoid dead legs with insufficient flow which promote Legionella) and mode of operation (e.g. what building/usage – process plant, commercial, domestic, etc.) should be carried out to ensure efficiency and safety. All steps presented in this article are a recommendation. To ensure particular


chemicals and procedures are suitable for your equipment, always refer to manufacturer instructions.

Corrosion – chemical or physical protection?

From a system point of view, good design and operating conditions with a well- planned pipe layout and flow velocities build the first step to corrosion control. Additionally, regular maintenance and monitoring are necessary. If corrosion is of concern due to high conductivity and chloride levels, chemicals are available which are safe for use in drinking water systems. Other options are powered/sacrificial anodes, or vessels made from stainless steel to protect water heaters and hot water storage tanks from corrosion. When it comes to material choice, the potential difference between metals is also important to consider. When more noble and less noble metals are used in the same system, the corrosion risk is higher.

Considering bacteriological water quality

Microorganisms can gather easily on rougher materials, although smooth surfaces aren’t ‘immune’ to this problem either. When this accumulation of bacteria (biofilm) gets out of hand, biofouling develops. Microorganisms feed on organic and inorganic substances contained in the water and can multiply rapidly. When corrosion is present, dangerous pathogens in the biofilm have an

32 October 2018

even better chance to thrive. One of these are Legionella bacteria. For this reason, the system design should avoid dead legs where they can grow under favourable temperatures (20-45°C). Following HSG274, hot water should be stored at 60°C or higher and distributed at 50°C or higher (55°C in healthcare premises). In water heaters, a built-in legionella protection cycle which automatically heats up the water to this temperature at certain intervals can provide safety. To avoid scalding incidents, thermostatic mixer valves (TMVs) need to be fitted.

first step to hot water system design is choosing the right equipment and material based on water quality and composition to prevent problems. A water analysis can help determine the choice of materials, the future

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