How to Build a Watermaker for a Boat

Boats often have a ready water supply, but cleaning it to make it drinkable can be a challenge. The process at sea or on freshwater rivers and lakes is more complex than just dropping a chlorine tablet in a bucket of water. Particulates, chemical pollutants and seawater salt must also be removed. This necessitates a multistage approach using carbon filtering and reverse osmosis.

Things You'll Need

  • 12-volt power supply
  • Reverse osmosis water pump, 30 to 50 psi, low voltage
  • Sediment filter
  • Pre-carbon water filter
  • Reverse osmosis water filter – 50 GDP
  • Post-carbon water filter
  • Component mounting box
  • Mounting screws
  • Water delivery hoses, 1/2 inch by 20 feet
  • Hose end screening attachment
  • 10 hose clamps
  • Water collection tank
  • Switch
  • Hose hanger bracket and mounting screws
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Instructions

    • 1

      Position the four filter stage components in the mounting box and mark where you need to drill the holes for the mounting brackets. Leave room for the pump between the pre-carbon and reverse osmosis filters. The filters should be positioned in the box from left to right so that the sediment filter comes first. It may be a simple screen filter, diatomaceous earth or sand filter. Screw it in place.

    • 2

      Attach the pre-carbon filter by its brackets to the box to the right of the sediment filter. Next to it, attach the low voltage pump and the reverse osmosis filter with the mounting screws that come with the units.

    • 3

      Attach the post carbon filter to the far right in the mounting box. Cut a supply hose to the length needed to reach from the outlet of the sediment filter to the inlet of the pre-carbon filter. Attach the hose with hose clamps. Cut a supply hose to the length needed to reach from the pre-carbon filter outlet to the inlet of the low pressure osmosis filter pump. Attach the hose with hose clamps. Continue cutting and attaching hoses from the pump to the reverse osmosis filter, from the RO filter to the post-carbon filter and finally from the post carbon filter to the collection tank.

    • 4

      Find a spot on the boat to mount the water collection tank. For stability in smaller craft, find a place low and close to the center so that as the tank fills with water it increases the stability of the boat. A multi-stage RO filter system with a pump with these specifications can produce 35 gallons of water a day a significant weight factor in even a medium sized sailboat or motorcraft.

    • 5

      Attach enough hose to the input of the sediment filter to reach the water from wherever you mount the component box. Attach the pre-screen to the open end of the tube to prevent large bits of organic material and trash from being pulled up into the tube.

    • 6

      Attach the power supply to the leads on the low pressure pump. Attach the negative lead of the power supply to the negative lead of the pump. Attach the positive lead to the switch. Mount the switch on the outside of the component box and attach the switch to the positive lead of the pump. The power supply output needs to match the power requirements of the pump. Most are 12 volt output for boating applications and to work with standard marine storage batteries.

    • 7

      Close up the component box once all the elements are in place and mount the box in a secure place on the inside of the boat. Attach the hose hanger next to the component box for storing the collection hose. When ready to make water, drop the hose over the side and switch on the pump.