Water stagnation

Since chlorine is removed from water by the carbon, extra care is required from here on to protect against bioburden growth. Carbon beds themselves are good breeding grounds for bacteria. To keep the system in check, a recirculation system as depicted in Fig. 3 is recommended. The constant recirculation avoids water stagnation and reduces viable bioburden growth. 

Even at these rejection rates, the dirty side of the membranes rapidly build up undesirable bacterial concentrations. To alleviate this potential problem, the membranes are normally automatically flushed on a continued cycle basis, say 3 to 8 minutes every four hours. Full sanitization with a sanitization chemical like phosphoric acid is required periodically based on continual monitoring of pressure drop, conductivity and bacterial count. To further reduce bacterial count, RO systems should be sized for 24 hours per day operation to minimize water stagnation. 

In common surface and groundwaters copper occurs only in tens of g. Water stagnating in copper piping can contain even units of mg 1. Acid waters from the vicinity of ore deposits contain high concentrations of copper ranging from tens through hundreds of mg 1 . ... 

Finally, exposure conditions of horizontal surfaces or surfaces subject to water stagnation in the splash zone of marine structures or structures in contact with de-icing salts, are extremely aggressive. 

A highly stratified water column with bottom water stagnation without oxygen renewal, which would increase organic carbon preservation. 

Water traps are low sections of the piping system where water stagnates and causes corrosion. Pitting corrosion occurs in water traps. This form of corrosion can be countered by minimizing the low sections through slanting the pipe or by installing drain valves at low points that are periodically drained. 

Are there connecting pipelines in which water stagnates for long periods and becomes colonized with germs (e.g. pipes which supply gardens or connection branches ready fitted for future pipeline extensions) ... 

Water stagnation zones within the vessel are avoided. 

In the UK, the lead leaching from brass manifolds was investigated by filling with a range of test waters and measuring lead concentrations after a range of water stagnation periods. 

As a guide, a moderately plumbosolvent water (e.g. a high alkalinity groundwater that has not been phosphated, or a low aUcalinity water that has been pH adjusted to 8.0-8.5 but not phosphate dosed) will often be described by M = 0.1 and E= 150. For 12 mm internal diameter lead pipes, the equilibrium concentration (E) is predicted (Hayes, 2002) to occur after about 8 hours water stagnation, consistent with the observations and predictions of others (Kuch and Wagner, 1983). 

While high-flowing water may still develop MIC, avoid designs that promote water stagnation. Design for flow velocities higher than 1.5 m/sec. 

The iron content of the treated water entering supply is very low, at about 20 pg/1, but does increase to cause iron discolouration problems in some parts of the distribution network, particularly at the extremities where water stagnation times within old cast iron water mains can be more significant. Occasional spikes in iron can result in intermittent particulate lead problems at some premises. 

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