Safe drinking water on board!

Safe drinking water on board!

Water is an important, basic and vital resource. We can survive a few weeks without food, without water a few days at most. Reason enough, therefore, to give water on board the necessary attention and to look at drinking water treatment on boats. In this guide you will find answers to the most important questions about drinking and fresh water supply on board.

What to know when it comes to drinking water supply on board

Even though most of us are amateur boaters who are unlikely to be in a situation where we are really dependent on the water supply on board, we should always have fresh drinking water on the boat. It is essential to ensure that the fresh water tanks are cleaned regularly and that the water in the tanks is treated correctly. You should test your drinking water at regular intervals to ensure that the fresh water on board is of good quality.


Why do we need water on board anyway?

It's probably the same for all of us: we need water for drinking, cooking, washing up and cleaning.

Different types of water can be used for different tasks, depending on the size of the boat and the requirements of the skipper and crew. I remember very well how, as a dinghy sailor in Holland, I just used to wash my dishes and cutlery in the river water, without really caring about of all the things that were in the water in a regular harbour in the 90s.... That said, I think we can agree that river water is perfectly adequate for scrubbing the deck.

Drinking water

What options are there to provide sufficient fresh water on board?

We have three basic ways of getting water on board: water from an external source, water from our tanks and water from bottles.

Water from an external source: Rainwater might sometimes seem like a viable option for drinking, however, it's not good for us in the long run, because rainwater lacks almost all the salts and minerals that our bodies need. In this case, it makes more sense to consider water treatment. You'll find information and tips on how to do this in the guide below.

Bottled water is easy to get hold of and uncomplicated. Usually it has a best-before date which should not be exceeded, if possible. Having a few bottles of water on board never hurts, and, depending on the sailing area, sometimes is required for insurance purposes. Storing bottles of water on board can give peace of mind, however, more and more sailors tend to refrain from plastic bottled water. Hopefully, the times when vast quantities of small bottles and cans ended up clogging our oceans are over. After all, environmental protection has also made an impact on sailors.

Water in drinking water tanks is the linchpin of our on-board water supply. Practical, quick to hand, convenient. That's how we want it, basically like at home. If....yes, if only it were that simple. Tap water is extremely likely to be safe to drink in northern Europe. But what about water that may have been stored in a tank for weeks? Not only can this water taste old and musty, but it can also make you pretty sick and cause nauseous gastrointestinal problems. That is, unless you take steps to prevent it from happening. Because algae can quickly grow and bacteria can multiply in your pipes, which is pretty bad.

When abroad, the drinking water supply from water tanks is often fraught with completely different challenges. Before taking drinking water from harbours or taps in other countries, it is advisable to find out about the local drinking water quality. Chlorine is often added to tap water, especially in southern countries. This makes the water on board undrinkable. You can often find information on this topic on the homepage of the Ministry of Foreign Affairs or similar institutions in the respective countries.

TIP: Carbon filters or active carbon filters can be easily "coupled" between the hose leading into the tank and the tap on the jetty using a Gardena adapter. This makes it easy to "filter out" the unwanted chlorine and fill up your fresh water tank without worry.

How can I test drinking water on board myself?

To avoid nasty surprises, there is a reliable and simple way of doing this, and drinking water tests are available in many forms and variants. To test the drinking water on board, test strips are used to check the chemical content of the water and test plates are used to determine the biological quality. Test results are usually available after a few minutes to put you at ease when it comes to drinking water on board.

What water treatment options are available on board?

To prevent contamination of drinking water on board, there are 3 ways to sterilise drinking water:

1 Boil the drinking water:

This is a simple and also very safe method where you boil the desired amount of water on board for about 10 minutes to kill any bacteria that may be present. Nevertheless, the water should also be filtered.

2 Sterilise the drinking water:

The most common way is to add a sufficient amount of water purifier in powder or tablet form to the water when filling the tank. Such agents, such as Aqua Clean, Mikropur or Mikrosept, ensure that the water in the tank stays fresh for up to 6 months by adding silver ions.

However, silver-containing agents for water disinfection should be treated with caution: the European Food Safety Authority has recommended a limit of 0.05 mg silver per kilogram of food. However, the WHO considers silver concentrations as low as 0.1 mg/L to be tolerable and without health risk According to the German Drinking Water Ordinance (TrinkwV), a list of permitted treatment substances and disinfection methods has been developed, and only substances that are included in this list may be used. Water sterilised in this way is allowed for personal use, but for this purpose only. Therefore, officially, we are not allowed to help our neighbours out with water from our tank.

Water filters

3 Water filters on boats:

Silver balls, which are added to the tank also work according to the same principle as sterilising agents containing silver. Here, however, great care must be taken to ensure consistency between the size of the tank and the respective agent.

A second tap in the pantry, through which only filtered water flows, is a good addition or alternative. Here, a filter cartridge with a replaceable freshwater activated carbon filter is then connected upstream, which ensures for at least one season that floating matter and most chemicals, such as chlorine, bacteria and germs, among others, are removed from the water. Such fresh water filters are available from Whale, Yachticon or Atlas. They can easily be fitted into the water supply and do not require much space. A T-connector in front of the galley tap, then a filter, followed by a small fresh water tap next to the sink, a set-up like this fits under almost any sink.
The other taps on board can then be used for simple tank water, not for drinking. As a precaution, an appropriate disinfectant should be added. Without chemicals, the water in the tank will sooner or later become undrinkable and unsafe to use, even for showering.
Of course, you can also install a water filter in the main water line of the boat, which would then filter all the water on board. However, the filter will then also wear out much faster. The filter capacity of an activated carbon filter is given in litres. Normally, replacing the unit once a year is more than enough.

Which water can be treated on board?

In general, you can treat tap water as well as salt water or brackish water (a mixture of fresh and salt water). There are several ways to do this:

Water with a watermaker

Producing drinking water with a water purifier is certainly the most interesting method for us skippers. In an idealistic world, it can allow us to be virtually self-sufficient, with no reliance on external supplies at all times. Without blowing the trumpet too hard for this: if you don't want to use chemicals to conserve water, don't like drinking stale water, don't feel like lugging bottles around with you and travel all over the world, then a watermaker, also called a desalination pump, is simply the solution to all your problems. Such a watermaker for boats can, depending on the design, turn almost any water into drinking water. The more laborious the pump has to work (i.e. dirtier the water), the sooner the pre-filters have to be renewed. In this respect, you should use the cleanest water possible. Deliberately using dirty water would be counterproductive and therefore expensive.

A desalination pump is not complicated: A watermaker contains a very fine-pored filter (semi-permeable membrane) through which the water to be purified is pressed at high pressure by an electric water pump. Clean, desalinated, pure water is then collected on the other side of the membrane. This water will not contain any viruses or bacteria, as long as the watermaker is properly maintained and in good condition. For smaller needs there are also desalination pumps with a hand pump and very small filters. However, these are mostly intended for hiking enthusiasts carrying lighter loads.

Even if there are barely any electronics or technology in a watermaker that could be prone to failure, there are still important points that must be observed without fail: since we are talking about a very, very fine-pored filter, the danger of "clogging" is always an issue. And it is precisely this fine-pored filter membrane that is the most important, most sensitive and therefore also most expensive component of such a system.

Filters for drinking water purifiers

A long series of pre-filters reduces the risk of clogging the desalination pump membrane. Depending on where the desalinator is located, different configurations are possible. Typically, a desalinator starts with coarse filters upstream, gradually the water is filtered through finer and finer pores in various stages of filtration up to the active carbon filter and thus becomes physically cleaner and cleaner. At the end of the chain, so-called "reverse osmosis" takes place on the thin membrane of the desalinator. Here, only about 20% of the incoming water becomes pure drinking water. The rest is needed to rinse the membrane and is then pumped back overboard. Drinking water filters are then changed about once a season, or more often depending on use.

Drinking water filters for boats are available in every size imaginable. Drinking water filters for recreational boating are fairly manageable in terms of size and the effort required to install them: they are about the size of a water tank and can be installed and stored with only a little skill and care. The most complicated part of fitting them is cutting a hole in the hull, which is necessary so that seawater can be sucked in and then cleaned by the filter. This hole should be as deep as possible below the waterline. If you aren't sure of how to do this, you should consult a shipyard or similar.

What kind of water tanks are there for drinking water on board?

It starts with the tank: available in plastic or stainless steel, flexible or rigid. Nowadays, any tank declared as a drinking water tank must be odourless and tasteless. Flexible plastic tanks are excellent for use where space is limited. When empty, they can fit through a maintenance hatch or in a storage box at the back; when full, they can be expanded to suit requirements. Fixed tanks are easier to handle if they have an accessible inspection door. They are easy to fix and lock so that they do not start moving back and forth in rough seas.

Drinking water on board

Where should drinking water tanks be located on the boat?

Stainless steel tanks are often already on board and an integral part of the hull structure. During installation, great care should be taken to ensure that the connections to the tank are not under any stress. Should such a connection be broken or come away, the consequences could be devestating, or in the least not pleasant. As a general rule, water tanks are best mounted in the area of the boat's centre of gravity so that they do not affect the trim of the boat, regardless of how full they are. Tanks should also be light-proof to prevent the formation of algae.

How are fresh water tanks cleaned on board?

Water tanks must be clean! Water that is kept in a bad state is pathogenic! If you fill up with fresh water, it will not stay fresh for long if there are residues of 'bad' water in the tank. Regular cleaning of the drinking water tanks on board therefore makes sense. It is sufficient to do this once a season. The best way to do it is mechanically through a maintenance hatch. If this is not possible, there are also some chemical cleaners on the market that do a good job, such as Yachticon's Water Tank Super Cleaner or Clean A Tank. This mixes an aqueous solution that is pumped through tanks and pipes and, after a certain time left to work, flushes algae and debris from the system.

What should be considered when winterising a water tank?

Before winter storage, the freshwater system must be completely drained. Frost can lead to valves and pumps bursting. This is because the water left in the system expands when it turns to ice. The only thing that can be done to help in this case is to empty all pipes, tanks and pumps completely or to use antifreeze in the water tanks.

TIP: Compressed air is a great way to really get all the water out of tanks and pipes. A small, portable compressor does a good job here. An alternative to completely emptying the pipes is to fill the system with drinking water antifreeze, which is pumped through the tank or directly from the tank through the pipes to the taps.

Fresh water pumps on board

Every time a water tap or shower is used on board, a pump is needed to transport the water from the tank to it. For drinking water, pumps are rarely submerged in the tank. Today, so-called 12- or 24-volt pressurised water systems are mainly used, which operate by means of an electric pressurised water pump. Well-known manufacturers offering pressurised pumps are Shurflow, Jabsco, Matro, Flojet or Johnson. These pump water from the drinking water tank into the on-board system. When a valve or tap is then opened, the pressure causes the water to flow. The pump then detects the drop in pressure and pumps new water from the tank into the system until the desired pressure is restored. When the tap is closed, the pressurised water pump then runs for a short time. This can give us the same "water tap comfort" on board as at home. When sizing a pressure water pump, the number of taps must be taken into account. The more taps you want on board, the higher the flow rate of the fresh water pump. We are used to about twelve litres per minute at home. If you want to use several taps at the same time, the required flow rate will consequently increase.

Hose connections for fresh water systems

When installing your on-board water system, be sure to avoid garden hoses or plug adapters. There are tested drinking water hoses that, thanks to their design, give microbes and algae no chance to multiply. These hoses are usually blue for cold water and red for hot water, contain no plasticisers and are odourless and tasteless. Fixed pipes with smart connectors are preferable for larger boats, such systems are available from Whale, for example. Dirty water hoses are usually white and also have an odour barrier layer for waste water and toilet water disposal. Basically, the same rule applies to installing a hose on board as for a house: care must be taken, after all, this is the most important element of all.