Boat Winterization – How to Winterize Fresh Water & Raw Water Systems on Your Boat

boat winterize fresh water

How to select the right marine antifreeze and properly winterize all your boat’s fresh water systems to ensure no freezing during winter boat storage

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When the temperature starts to dip in the northeast where we boat we know its about time to start preparing our boat for winter storage. And the first step is usually loading our dock cart up with a case of pink (marine antifreeze) to winterize our boat’s fresh water systems.

Some boaters leave all of their winterization up to their marina service department, but we like to do all of it ourselves. We’ve been boating for 20 years and have the process pretty much down, so we feel more comfortable knowing that everything is done properly before winter storage.

Note: Much of this process could also be followed for anyone winterizing their RV fresh water system!

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Choosing the Right Antifreeze for Your Boat

The first step is picking up some bottles of marine antifreeze (AKA “Pink”). We usually need a few cases – one for our fresh water systems and then one for our engines, generator and A/C.

If you are getting antifreeze to use in your fresh water systems AND your engines make sure the bottle says it can be used for both. The green or orange type of antifreeze that goes in your engines is made with a toxic substance called ethylene glycol that would be poisonous if accidentally ingested… so it should NOT be used in your fresh water systems!

Marine antifreeze is made of a substance called propylene glycol – its non-toxic and doesn’t hurt the environment. We typically choose marine antifreeze for -50 degrees and buy (2) cases of 6.

Winterize Boat’s Fresh Water and Raw Water

There are four different kinds of water systems on a boat that need to be addressed for winterization:

  • Fresh water  – water coming into the boat from water hook-up or tank filling for sinks, showers and heads
  • Raw water – water systems that take water into the boat (from lake, river, etc) like engines, generator or A/C
  • Gray water – water systems like the drains and shower sumps
  • Black water – head tank

To winterize the fresh water system, some of the basic steps we need to do include:

  1. Empty out the fresh water tanks
  2. Fill fresh water tanks with several bottles of marine antifreeze (we use 6 for our 41 ft. boat)
  3. Turn on fresh water pump to run water through sinks, showers, wash down shower/hoses, etc. until you see the water change from clear water to pink water
  4. Empty the hot water tank and run hot water through all systems until the water changes from clear to pink
  5. Pour antifreeze down the shower drains into the sump pumps
  6. Get a final pump-out and then flush antifreeze down the heads

WATCH VIDEO: Captain Brian shows you step by step how we winterize our fresh water systems in this video:


In the next phase of our boat winterizing, we winterize our hot water tank, engines, generator, a/c and sumps with marine antifreeze. This completes our winterization of fresh, gray, raw and black water systems for our boat.

WATCH VIDEO: Captain Brian shows you step by step how we winterize our hot water tank, engines, a/c and sumps in this video:


Finally, preparing your boat cabin for winter storage is important too!

WATCH VIDEO: Check out how we pack up our cabin, defrost our refrigerator and ensure our interior is ready for winter storage in this video:

Boat Winterizing Products Used

Here are some of the products we use or recommend to use during boat winterization:

Marine Antifreeze -50 (water & engine) 6 Gal pack 

Boat Winterizing Kit for Engines

Expandable Hose

DampRid Buckets

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Diane Seltzer

View posts by Diane Seltzer
Diane is the founder of as well as the boating lifestyle site for kids Active in the boating industry, Diane has also led the marketing for multiple recreational boating businesses and startups.
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