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Watermakers use a process called reverse osmosis to produce fresh water. This happens by using a high pressure pump to force salt water through a semi-permeable membrane which lets fresh water molecules through, but keeps other larger contaminants like salt, bacteria, minerals and organisms out. The leftover “brine” is then discharged overboard while the pure fresh water is diverted into your water tank. Low temperatures or high water salinity can cause a significant decrease in the actual output of the unit – so make sure to take your cruising environment into consideration when reading through the manufacturer's specifications. It's also extremely important to follow the manufacturer's directions for usage and to make sure you preform a fresh water flush after every use with chlorine-free water. Curious to see exactly how good the water you are making is? Most units now come with a TDS (total dissolved solids) meter built in – but if not you can purchase one to check the quality of the water before putting it in your tank.
Now that you've decided to add a watermaker, the first thing you need to figure out is how much water you use onboard on a daily basis. Try to estimate how much water you use for everything on your boat – including water for drinking, cooking, washing dishes, cleaning your hands, showering and doing laundry. Once you've got your number – multiply it by how many people will be onboard and you should have a good idea of how much water you will be using on a daily basis. It's important to note that the amount of water you use can be highly influenced by the climate you are in and the activities you enjoy while boating.
We should also point out that most manufacturers calculate their unit's output in gallons per day – so you'll need to convert that to hours to see if the unit will accommodate your needs since it's highly unlikely you'll be running it 24/7.
The size of watermaker you need isn't just about how much water you use – it's also about how long you will go without access to fresh water sources. If you are a coastal cruiser, chances are you can usually find a reliable water source at least once a week to fill up your tanks – so you can buy a smaller output watermaker. But if you are planning to take your boat offshore and need to be completely self-sufficient – you may need a unit with higher output.
Most modern units offer electronics that automatically perform a fresh water flush after use or inactivity – while some require the manual manipulation of valves – so you need to ask yourself if you want control or if you prefer the unit do all the work. If you are the kind of cruiser who likes to "set it and forget it" then the fully electronic option is definitely the way to go.
Another major point to consider is what your options for powering the unit are. Watermakers come in three different types – DC, AC or engine driven – all of which have their own pros and cons.
Before making your decision you need to investigate how easy it is to obtain replacement parts and whether the manufacturer supports the area you will be cruising in – especially if you plan to cruise to other countries. You should also investigate if the unit uses a standard size membrane (making it easier and cheaper to find replacement membranes no matter where the boat is located) or if it uses a proprietary size membrane (which means you can plan on spending significantly more when it comes time to replace it).
You should also consider how easy is it to service the watermaker and its pre-filters before making your choice. Most modern watermakers have incorporated fresh water flushing and water testing – a great addition – but make sure you can still access the areas that need to be serviced after the unit is installed. This is especially important as manufacturers move to more “enclosed” style units over modular designs.
Once you've taken a look at all of this, you should be ready to move forward and make a purchase. Fisheries Supply is proud to offer several brands of watermakers for a variety of needs – including FCI, Katadyn and US Watermaker. We hope you've found this overview on buying a watermaker helpful – but if you have any additional questions, please don't hesitate to contact our product experts at (800) 426-6930.