Requirements for fresh water tanks are different than black water or grey water tanks. Fresh water tanks are designed with the following features:
  • Most tanks are gravity fed to a hand pump or a low volume electric pump and therefore do not see the high vacuum pressures which waste tanks may encounter.
  • However, during the filling of the tank most marinas use city water pressure. City water pressure can be as high as 80 psi. allowing for damage to occur during filling if the tank vent is blocked or restricted.
  • Stocks sized molded tanks work well for water tanks and are typically made from standard HDPE (High Density Polyethylene). Polyethylene is quite odour free and tends not to harbor bacteria. Custom tanks can be made using standard HDPE or we can use a hybrid material such as HMW-PE (High Molecular Weight – Polyethylene) which is more resilient (it has more stretch even in sub zero temperatures).
  • Black Sclair pressure rated water pipe can be used to store drinking water. This is a NSF certified pipe made from pigmented PE by KWH. From KWH – PE Pipe manufacturer’s opens in new window

Is Sclairpipe certified for potable water use?

Yes. KWH stamps Sclairpipe piping or fittings used for potable water with the initials NSF. This means the product conforms to NSF Standard 14 “Plastic Piping components and Related Materials” and Standard 61 “Drinking Water System Components-Health Effects”. Pipe marked with CSA logo and “CSA 137.1” initials is also suitable for potable water use.

Rethinking Your Water Tank Requirements
Custom tanks can be designed to maximize living space; tall rectangular or cylindrical tanks can be placed in corners, in compartments, under seats, in seatbacks etc. Since fresh water tanks don’t contain solids, tanks can be made long and slim. (a 4” diameter pipe x 48” long will hold 20 liters (5 US Gal) of water. Changing the location of your freshwater tank can make room for more holding or water tank capacity.
How-To Menu

Typically the outlet on a fresh water tank is at the lowest point of the tank allowing for gravity drainage to minimize standing water during storage. Outlet should be at least .75 NPT a 1” is recommended. Since this fitting is below the water line we also recommend that a welded tank boss be used.

The tank inlet or fill port should be mounted on the top or near the top of the tank. The inlet should be a .75 NPT. We recommend that welded tank bosses be used in all fresh water tank ports since it reduces the areas that bacteria and dirt can be trapped (such as between the gaskets in bulkhead fittings.).

The tank vent should be a .75” NPT outlet and should be mounted at the highest point on the tank.

An important feature we try to incorporate on all our tanks is a 4” o-ring sealed inspection port; this allows easier access for cleaning the tank.


You can make a sketch of the tank you require. Place some basic dimensions on the drawing and if you would like to fasten the tank to a wall, cabinet or other location it is important that you make a rough sketch or send us a picture of the location. We can weld on brackets that can be used to secure the tank to the boat. We will provide you with our drawing of the tank for your approval before we make any tank so you can verify the dimensions.

Unless you are sure that the new tank size will fit into the location, it is a good idea to make a full-scale cardboard mock up of the tank and put it in place.  There is nothing more frustrating than to get a new tank and not be able to fit in place because it is a bit too large. The mock up can be pieces of cardboard duct taped together at the seams. Make sure to mark the locations of the inlets, outlets, vent and possible the location of the access port.

It is important that you are able to get the full size mock up out of the boat. Sometimes you underestimate the cabin opening and the new tank cannot fit in the boat.

If you are shipping the mock up to us, please mark the adjoining pieces at the seams – “A,A” – “B,B” etc. and then take a picture of the tank.  You can now cut the tank at the seams and lay it flat and package it for shipping to us at any of our locations.


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