Drinking water quality and bacteria in water distribution systems (Part 2)
In Part 1, we looked at bacteria and viruses in water, common water treatment techniques to manage bacteria in water and common waterborne pathogens. In Part 2, we consider how pipe material, pipe age, the physical integrity of the water distribution system, the number and type of water storage systems, and water chemistry and flow may influence drinking water quality. We also look at water safety and disinfection strategies designed to protect water distribution systems and human health.
Water distribution systems – pipe material will impact water disinfection strategies
Water distribution systems in buildings are largely unique to each structure. Water pipe material utilised will often vary from building to building and within individual systems. New pipes are often constructed from PVC or lined, while older pipes are generally manufactured from different material, lined or unlined.
Fixings and installation quality can dictate system integrity, corrosion rates and aeration, flow and pressure. The composition and condition of these pipes can influence what chemicals may be released in to the system and the types of bacteria that colonise within water distribution systems and on pipe surfaces. Some pipe materials release bio-source compounds (iron, hydrogen and phosphate for example) that can encourage biofilm growth and multiplication of bacteria.
Biofilms coating the interior surfaces of water distribution pipes often develop slowly and can take years to reach maturity. Old pipes can become heavily tuberculated, with depths of scale and rust exceeding 10 centimetres providing an even greater surface for biofilms to populate and providing an ever-enlarged source of nutrients for biofilm to draw from. Chemicals treatment used to coat water distribution pipe interiors to control corrosion, scale and destroy biofilm work differently and can have different effects on biofilm. Some phosphates for example can stimulate bacterial biofilm growth and re-growth, while some silicates can inhibit it. GENOX generating NEUTHOX®, is an HOCl which is a particularly effective way of controlling biofilm. Approved for drinking and process water, it is equally effective across most type and ages of water system pipe.
The physical integrity of the water distribution system
Water leakage from UK pipes is over 3 billion litres a day according to the Consumer Council for water (CCW). Breaks and leaks in pipes can lead to low water pressure events which help bacteria cling to surfaces and may encourage biofilm growth. Soil microbes can invade and colonise the water distribution system. Sediment that enters, may serve as a source of nutrients (see common contaminants in water). New pipes and alterations to pipework may impact system integrity, pressure, flow rates, aeration and plumbing events and major incidents may require water distribution systems to be treated with emergency disinfection strategies and special sterilisation and flushing. The Ultralox (skid) for example can be used for critical applications and highly effective mobile disinfection as well as mobile ClO2IX Catalytic Generators for fast, reactive responses to trigger events.
The different type of storage facilities including cold water storage tanks can also impact hydraulic pressure and water age. Water tanks are common habitats for water microbes. Systems with large and multiple water tanks can lead to more and older water existing within a building water system and this can lead to decreased disinfectant concentrations and, increased sediment accumulation and therefore influence microbial growth.
Water chemistry – source, stability and temperature and how it impacts water quality
Source water - nutrients in water will influence water microbiology. Microbes feed on compounds and carbons and nutrients found naturally within water and this becomes more important with water re-use as disinfection concentration becomes impaired over time. There are increasingly sophisticated and sensitive water laboratory testing services that can help determine what exactly may be happening in your water chemistry and lead to better decision-making when it comes to water treatment and secondary disinfection.
Chemical stability - water changes once treated and can respond in ways that favour microbiological growth. For example, disinfectant residual effectiveness can decrease at rates depending on water temperature and disinfectant dosing. Ammonia is released from the chloramine residual as it decays. Haloacetic acids and other disinfectant by-products can provide a source of nutrients for some microbes to grow.
Byproducts – such as chloramine can encourage bacteria in water growth.
Temperature – microbiology in water is heavily influenced by temperature. Different organisms respond differently to changes in temperature and seasonal temperature changes – which is why disinfection regimes are often stepped up or change in hotter periods.
Water pressure, turbulence and flow rates
Changes in water pressure, turbulence, flow rates and flushing regimes can all impact the existence, re-growth and lifecycle of biofilms in the water distribution system. System design, the age of water, the pressure and circulation rates of water, will all influence the effectiveness of disinfection strategies and water microbiology.
Useful questions (checklist):
- Do I know precisely what water chemistry is going on in my building(s) that may affect water quality?
- Do I need a Water Safety Plan?
- Is drinking water and potable water at risk from contamination (water system integrity, private water supply source water etc)?
- What do I care most about when considering primary and secondary water disinfection method and safety (see most common 9-criteria)
- Do I know precisely what water microbiology is occurring on site?
- Which microbiological control measure(s) are best suited for my application / building(s)?
- Are new-style ClO2 chlorine dioxide generators all they claim to be?
- What low hazard, low concentration, non-ClO2 disinfection strategies are available to me?
Protect your water. Download the 'Water safety, disinfection and secondary disinfection' eBook.
Written by Alex Winter
Alex is a Marketing Contributor and has 5+ years in water treatment and ACoP L8 compliance and works across all six linked areas of the business; Water Treatment, Waste Water, Water Hygiene, Air Hygiene, Engineering and Legionella Training.