Water tank cleaning: the basics
Water tank cleaning is important and complicated because pollution and biological contamination in drinking water tanks can have many causes. However, these can generally be divided into three categories:
- Dirt ingress into the drinking water chambers due to construction/conversion work (e.g. sludge/fecal matter), floods and/or animals such as mice or similar (direct pollution/primary contamination)
- Contamination of drinking water tanks or spring tappings resulting from use of unsuitable materials (e.g. pipes containing plasticisers that promote microbial growth), thread grease, lubricants or foreign materials such as rags, sawdust, etc. (indirect pollution/secondary contamination)
- Contamination due to chemical/physical/biological factors (e.g. limescale deposits), which are conducive to biofilm growth. (Exponential source of contamination)
All of these factors share one thing in common — they can act as sources of repeated contamination. In other words, there may be sites within the drinking water system that continuously contaminate the water with microbes. This is virtually unavoidable in points two and three above. In addition, the problem is exacerbated in all three cases by the fact that even disinfection of potable water storage tanks with high doses of disinfectant usually only serves as a temporary remedy.
Cleaning and disinfection of drinking water tanks in the event of direct contamination.
Direct pollution is often the result of flooding, whereby mud, soil and microbes overflow into the drinking water chambers or spring tapping. Alternatively, improper spreading of manure in the water protection zone can result in contamination. This is characterised by cloudy water, changes to its taste and sudden, high concentrations of microbes — in particular, a high number of fecal germs.
In such cases, although the contents of the drinking water tank are typically polluted and contaminated with microbes, the walls and pipes remain free from sediment/mucosal layers. For this reason, it is usually sufficient to drain the entire water supply system and spray the walls and possibly the pipes thoroughly with water (fire hose). Subsequent surface disinfection will remove any adhering microbes. The drinking water chamber can then be refilled, possibly with the addition of some disinfectant i.e. drinking water tank cleaning chemicals as a precaution. After the water tank cleaning, once the disinfectant has degraded, the water supply is ready to be reconnected to the network.
Drinking water tank cleaning and disinfecting in the event of indirect pollution / secondary contamination
The materials used in water supply systems are specifically certified to ensure their suitability for this purpose. Non-certified materials, such as all kinds of garden hoses, plastic parts, plastic films, etc. are sometimes also used in drinking water supply systems out of ignorance (especially in privately created spring tappings), which may have unpleasant consequences.
Many plastic parts contain plasticisers and other substances that promote microbial and biofilm growth in drinking water supply components. Cleaning and disinfecting these incorrectly designed drinking water chambers can provide a short-term fix for the problem, however the maintenance cycles necessary for these tanks are significantly shorter compared to other drinking water systems. The only effective remedy in such cases is to replace the problematic materials or possibly add inlays.
However, in the event of contamination with fats or oils, these substances can often settle and solidify on a surface or inside a pipe connected to the drinking water tank. Microbes can then multiply under this water-repellent layer, resulting in continuously high levels of bacterial growth (usually aerobic, mesophilic bacteria) in the drinking water chambers. If this occurs, the system must be cleaned using a highly alkaline drinking water reservoir cleaning solution (e.g. sodium hydroxide). The tank must first be neutralised with acid and then flushed with water before all surfaces are disinfected (see pt. 1). Smaller contaminants can also be specifically treated with an suitable disinfectant cleaner, such as SanoClean.
Water tank cleaning and disinfection in the event of exponential contamination.
The chemical composition of the water determines both the speed with which deposits are formed and their severity. These deposits usually consist of lime, manganese and possibly dissolved iron. While the deposits themselves are safe from a hygienic point of view, by creating rough surfaces on the walls of drinking water containers they act as an ideal “primer” for biofilms containing algae, mould and bacteria.
These deposits must therefore be regularly removed from the walls of the drinking water chambers. Drinking water tank cleaning chemicals, more precisely a strongly acidic special cleaner for water tank cleaning such as Sanosil TW, which can break down and detach the limestone layers, is ideal for this purpose. Rusty iron oxide deposits can be additionally treated and removed by means of antioxidants. Naturally, the acid must then be neutralised with an acid/base solution and flushed out. The surfaces and contents of the drinking water system are subsequently disinfected.
Drinking water storage tank disinfection: Tanks with smaller volumes
It may be possible to treat smaller tanks directly by means of shock drinking water tank disinfection. However, this only works if the source of contamination is “visible” in the drinking water chamber and not concealed by a solid layer of dirt — otherwise, this layer would shield the microbes from the disinfectants.
Procedure: a relatively high dose of water tank cleaning products (such as 500–1000 ppm Sanosil Super 25) is added to the contents of the drinking water chamber, spring tapping or tank, and mixed by means of a pump. Treatment time takes between four to twelve hours. The disinfectant solution is then drained and discarded. It is essential to ensure that this water is not accidentally used for drinking! After a brief rinse and, if necessary, a refill, the disinfection of water storage tanks is complete.