Fig 1.
Schematic of a typical water system.
A) Schematic of typical gravity-fed water system found in may commercial and older reseidntial buildings. B) Schematic diagram of a typical cold water storage tank as per WRAS Guidelines 1. Incoming mains with isolation valve connected to ball valve; 2. Inspection acces hatch situated above the ball valve to assist with maintenance; 3. Outlet of the tank with isolation valve.
Table 1.
Tank deatails.
Table 2.
Relative scoring.
Fig 2.
Sample temperature comparison.
Sample temperature (°C) of the incoming mains water (IM), under the ball valve (UBV) and at the far end (FE) of fifteen operational cold water and potable water storage tanks in different London Boroughs recorded during routine inspection and sampling between November 2015 and July 2016. The red line shows the regulatory threshold of 20°C (acceptable limit) used for routine monitoring.
Fig 3.
TVC analysis result comparison.
Comparison of Total Viable Counts (expressed as colony forming units/100 ml) from water samples taken under the ball valve (UBV) and at the far end (FE) of fifteen independent cold water and potable water storage tanks located in different London Boroughs, and incubated at A) 37 °C for 2 days and B) 22 °C for 3 days. Tanks were sampled between November 2015 and July 2016. ‘P’ denotes tanks designated for potable water storage. The red line shows the regulatory threshold for TVC in potable water tanks from samples incubated at 37 °C for 2 days.
Fig 4.
Comparison of Legionella and Pseudomonas analysis results.
Comparison of (A) Legionella species (expressed as colon forming units/litre) and (B) Pseudomonas species (expressed as colony forming units/100ml) in water samples taken under the ball valve (UBV) and at the far end (FE) of fifteen independent cold water and potable water storage tanks located in different London Boroughs. Samples were taken between November 2015 and July 2016. ‘P’ denotes tanks that are designated for potable water use. The regulatory threshold for Pseudomonas in potable water is zero (line not shown) and is 100 cfu/L for Legionella in tank water.
Fig 5.
Comparison of TVC and Pseudomonas analysis results.
Comparison of A) Total Viable Counts (TVC; 2 days incubation at 37°C) and B) Pseudomonas species (expressed as colony forming units/100ml) measured in water samples taken under the ball valve (UBV) and at the far end (FE) of potable water storage tanks located in different London Boroughs. Samples were taken between December 2015 and July 2016. The regulatory threshold (10 cfu/ml TVC and 0 cfu/ml Pseudomonas) is depicted using a red line.
Fig 6.
(A) Example of a 5 metre long GRP potable cold water storage tank showing the mains water inlet. (B) Sedimentation levels increase towards the far end (FE) of the tank from the inlet ball valve end (IBVE). The arrow shows the direction of mains water flow into the tank. Tank reference T10.
Fig 7.
Comparison of long metal tank and small plastic tank.
(A) 4 metre long metal cold water storage tank with butyl lining (T13) showing visibly clear stored water under the ball valve (A), compared to sediments and biofilm at the far end (B). (C, D) shows a 1 metre long plastic tank with visibly clear stored water (T15).
Table 3.
Comparison of TVCs, Pseudomonas and Legionella (cfu/volume) from UBV and FE samples.
Fig 8.
Position of inspection hatch and inlet on cold water storage tank.
A typical 4 metre long metal cold water storage tank with internal butyl lining showing the position of the inspection hatch and mains inlet to the ball valve.
Fig 9.
Comparison of LD cases in the USA and UK.
Average percentage of LD cases occurring in the United States and UK annually by month. U.S. census data 2000–2009 and UK census data from 2015 and 2016 relative to seasonal high temperatures (District of Colombia and average UK temperature). Census data reported to Centers for Disease Prevention and Control (CDC) through the National Notifiable Disease Surveillance System (NNDSS) and a Supplemental Legionnaires Disease Surveillance System (SLDSS). UK data on Legionnaires disease was acquired from Public Health England reports. Solid line represents USA and dashed line is the UK.