Drinking water on board: How to keep the water tank free of germs

Even if clean water is poured into the tank, it is all for nothing if the actual contamination takes place inside the water tank itself. Without continuous protective measures, it can take as little as a few days for a biofilm to form on the inside walls of the tank. Once established, a biofilm is very difficult to remove. It acts as a permanent source of a wide variety of pathogens. Even though this does not usually pose a risk, there remains a sense of unease that something could develop in the tank after all. As well as the traditional – yet equally tedious – method of cleaning with a brush and cloth, there are chemical treatments available to combat the biofilm.

More on this topic:

• ​​These methods will help you filter water properly
• ​Workshop: How to disinfect the on-board drinking water tank in four steps
• ​Market overview: Straight from the tank – drinking water additives
• ​Drinking water filters: How to get clean water into the tank

There are two basic strategies available: systems that remain in the water tank permanently and operate continuously, and chemical treatments that are added to the water when the tank is filled.

Silver ions have a long-lasting effect, but not to the same extent everywhere

In systems for purifying drinking water in tanks, the release of ions by silver is the most widely used principle. The products are placed in the tank either as a mesh or as a compact sphere. During use, the ion concentration in the water rises until the chemical saturation limit is reached. At this point, no further ions are released, so an overdose is impossible. Alternatively, there are metallic solutions such as the ae-aqua cartridges. These use a coated stainless steel wire mesh which kills germs via free oxygen radicals on the surface, and therefore requires no silver ions or chemicals.

Product Overview

What is more interesting is the distribution of the ions themselves. In still water, released ions only migrate through the water tank via a slow chemical process. When there are many small silver beads in a large tank, a high concentration builds up in the immediate vicinity of the silver source, whilst areas of the tank further away remain inadequately protected. Flat nets that extend over a significant portion of the tank floor solve this problem and provide a more even level of protection for the entire tank’s contents. However, when the ship is in operation and the water in the tank is in motion, this effect is largely cancelled out. During layovers in port lasting several days, however, this can become a problem.

Material compatibility must be taken into account

At the same time, one must also consider the materials used and check whether they are compatible with the chemical properties. For example, free silver ions can cause considerable damage in aluminium tanks. In systems with copper coils in the boiler, the copper components are also electrochemically oxidised and dissolved by silver ions. Anyone using silver must therefore be familiar with the materials used in their tank system.

​Under the current Drinking Water Regulations, the use of such preparations is now prohibited on commercial charter yachts and in the public water supply network. Whilst the method remains permitted for private owners, it raises questions regarding its medical safety. In this regard, the World Health Organisation (WHO) states in its Guidelines All-clear for drinking water quality: concentrations of up to 0.1 mg/l are classified as posing no risk to health. As the products available from specialist retailers are limited to a maximum of 0.08 mg/l anyway due to their physical saturation limit, most systems remain permissible for purely domestic use.

Chemical preparations are used for preservation or disinfection

In addition to hardware systems, there are also chemical products that treat the water in the tank directly: pure silver preparations, whether in liquid or tablet form, preserve the water and prevent recontamination. However, if the water is already contaminated, they have no effect.

​Combined chlorine and silver products work in two stages: the chlorine disinfects, whilst the silver ions then keep the water stable over a longer period. Products based on Neuthox technology, such as the liquid Blueway According to the manufacturer, Danish Clean Water disinfects and cleans the entire system in half an hour without using traditional chemical irritants. It is very important to note that limescale and slime deposits significantly reduce the effectiveness of all these products. Some manufacturers therefore recommend thoroughly cleaning the water tank before using the products, in order to enhance their effectiveness and prolong their lifespan.

​​Important: An effective preservation system is just one link in a whole chain. A good filter when filling the tank protects the tank from external contaminants, but cannot prevent the water from starting to spoil whilst the boat is moored for weeks on end in a warm hull. The preservation system keeps the water in the tank stable, but has no effect on the pipes between the pump and the tap, where biofilms can build up. A high-performance post-tank filter protects the tap, but offers only limited protection against bacteria that have long since taken hold in the tank and are spreading from there throughout the entire on-board system. The level of effort that is reasonable depends on the sailing area and how the boat is used.

Silver in the fuel tank sounds simple, but it can quickly become a matter of materials on board. Please let us know in the comments whether you rely on chemicals, hardware systems or regular tank cleaning.