Valve Sizing Tool

Biofilm removal by shear velocity

We’ve always been strong advocates of periodic high velocity system flushing to remove biofilm from the internal pipe surfaces of domestic water systems – in particular in large buildings such as hospitals and schools.

However, after reading this article 'Biofilms: when are bacteria really dead?’ in the May '14 issue of Clinical Services Journal, we’re now even more convinced that it should be part of a regular and documented water system maintenance regime.


The standard method for microbial testing is by water sampling then culturing the bacteria collected, for example Legionella and Pseudomonas. However, since around 95% of the biomass remains on the walls of the domestic water system, bacteria collected through water sampling only represent a tiny proportion. Not only that, Professor Flemming’s work has determined that bacteria can be in a VBNC state – Viable But Non Culturable, caused by a stress factor such as exposure to chemical or cold temperatures. Removal of the stress factor has resulted in resurrection of the pathogens and subsequent infection.

So, what’s assumed to be dead may not actually be dead...and what’s being sampled makes up less than 5% of the total bacterial count. The remaining 95% should be considered, therefore, to be a mass of pathogenic opportunity and as much as possible must be removed. How do we do that?   Draining upstream from the integral TMV and outlet flow regulator enables an increase in water velocity.   By elevating the water velocity, the established equilibrium is upset and shearing forces slough off excess biofilm, which is then carried away down the drain. The greater the change in velocity, the greater the shearing effect will be.  The video below demonstrates this process at an Optitherm thermostatic tap, after which we recommend disinfection using heat from the readily available hot water supply at 60°C.

Flushing kits for Horne TMVs, shower valve and the Optitherm are available as standard accessories.