Get your Freshwater System Ready for a Season Afloat

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As I knelt beside the open cockpit locker of my 36-foot Pearson cutter Sonata, I could hear the gentle whir of my freshwater pump. It didn’t sound normal. I reached down and felt the pump housing. The pump was in constant-cycle mode and running hot. It could pump until it burned out and still fail to pressurize the freshwater system I thought I had just finished commissioning.

I stopped the pump and began searching for loose hose clamps. I started with the least accessible ones at the freshwater outlets leading from the two main water tanks to the manifold under the galley sink. I knew from experience that a season of sailing and motoring, temperature extremes suffered during the winter, and undetected hose deformations at barbed connectors could cause a hose clamp to loosen just enough to allow air to enter a freshwater system without causing an obvious water leak. I’d already triple-checked the connections at the pump, the water heater, the in-line strainer and the accumulator tank.

Sure enough, some of the hose clamps under the sink were loose. A few minutes later, I flipped the pump back on and heard the heavenly sound of the system charging. Soon air hissed from the galley faucet, followed by a gush of water. My freshwater system was back in action.

Pressure water systems

Your boat’s pressurized freshwater system is fairly simple, but it can cause some headaches if you don’t know the basics when commissioning it. Most systems have self-priming electric water pumps that lift water from the tank. These pumps can be mounted above the waterline. Some water pumps are not self-priming and must be mounted below the waterline so that fresh water from the tank is always present in the pump body when the pump is turned on. All freshwater pumps have pressure switches that kick on when pressure drops below a preset level, normally about 30 to 40 PSI.

In most systems, an accumulator tank also plays an important role. These tanks are typically fitted with an internal pre-pressurized air bladder (though smaller ones may have no bladder). As water is pumped into the bottom half of the tank, air is compressed in the top half. When you first turn on a faucet, the accumulator tank maintains enough pressure to deliver water without immediately triggering the pressure switch in the water pump. Once pressure in the tank drops low enough, the water pump turns on and recharges the system. This reduces pump cycling and extends pump life.

Another part of the freshwater system you need to pay attention to during spring commissioning is the water heater. These normally are calorifiers with both an AC heating coil and a heat exchanger plumbed to the engine’s cooling circuit. You will also need to focus on any water filter or in-line strainer installed in the system.

Expelling antifreeze from all your plumbing lines is a key job when commissioning your water system. The goal is fresh, clear water running from every tap (inset)

Expelling antifreeze from all your plumbing lines is a key job when commissioning your water system. The goal is fresh, clear water running from every tap (inset)

Flushing the system

Commissioning your boat’s freshwater system consists primarily of making sure it is purged of any antifreeze that was introduced when it was decommissioned. Start with the water tank. Open the inspection port and pump or sponge away any puddles of antifreeze that may be present below the freshwater pickup. Wipe down as much of the inside of the tank as possible with a clean, damp rag to remove any old layers of sediment or algae. Once your tank is clear of antifreeze, fill it to a quarter of its capacity. If you have multiple tanks, repeat the process.

Now turn to the water heater. Chances are it was disconnected from the rest of the system to drain it during winterization. Before you reconnect it, make sure the circuit breaker for the AC heating element is turned off. Put some tape over the breaker switch. You don’t want to turn on the heating element at this point, lest you burn it out.

Your water heater is probably equipped with a magnesium sacrificial anode. You should check this every year at this time. Many sailors overlook this and subject the innards of their heaters to damaging galvanic corrosion. Check your owner’s manual for instructions on when your particular sacrificial anode should be replaced, and replace the anode if necessary. Heating elements are also subject to corrosion, so check them as well. While you’re at it, wipe away any sediment in the bottom of the tank and make sure the tank’s mounting feet aren’t loose. Then reconnect the water heater to the freshwater system.

Many water heaters (left) are equipped with magnesium anodes. These should be checked annually. Check the wiring on your pressure pump (right) and make sure it is firmly mounted in place

Many water heaters (left) are equipped with magnesium anodes. These should be checked annually. Check the wiring on your pressure pump (right) and make sure it is firmly mounted in place

Next check out your water pump’s electrical connections. All should be sealed with heat-shrink tubing, or at the very least with electrical tape, and none should be loose or obviously corroded. Check the pump’s mounting nuts and bolts to make sure they are tight. A loose pump will vibrate excessively, causing noise and possible damage. Reconnect any other hoses as necessary and tighten all hose clamps. Rest assured, some will likely be loose, which can cause water leaks and allow air to enter the system. Eyeball the hoses to ensure that none are collapsed, overly dirty or bent at acute angles.

After this is done, move on to your water filter. Dump out the antifreeze and thoroughly clean the filter housing inside and out, but don’t replace the filter element yet. You don’t want any antifreeze or water-treatment agents passing through it. Just fill the filter housing with fresh water. If you have an in-line strainer, clean that, too.

When all appears to be in order, turn on the water pump and open the galley faucet. You’ll hear air being ejected from the lines as the pump charges the system. When water flows freely, turn off the faucet. Your pump should turn off. If it does, move on and do the same with any other faucets aboard. If the pump won’t shut off, then you may have air trapped in the system, which must be purged. You may also have a water leak.

After the antifreeze in the pipes has been expelled and you see clear water running from all your onboard faucets, empty whatever is left in the tank and then fill it again, all the way this time, and add a tank and hose cleaner to kill bacteria, algae, mold and mildew. One tablespoon of household bleach for every 5 gallons of water in the tank is another alternative. Allow the cleaning solution to sit for several hours or up to a day, then pump it out. With a pump rated at 3 gallons per minute, you should be able to pump a 60-gallon tank dry in about 20 minutes. But don’t run the pump longer than 10 minutes at a time, as it can burn out if it gets too hot.

If you find your water is malodorous or tastes faintly of chlorine or any other chemicals, flush it again with a vinegar solution. Add one quart of white vinegar for each five gallons of tank capacity. Allow this to sit overnight, then again flush the system with fresh water.

Once you’re satisfied that your water is clear and clean, replace the filter element in your water filter. Purge the system once more to ensure no air is lurking within it, testing the hot- and cold-water faucets and any mixing valves. If the water pump cycles on and off at regular intervals when you draw water from the faucets and stays off when the system isn’t in use, you’re good to go for another sailing season.

Water System Commissioning Checklist

  1. Open your water tank’s inspection port and remove any standing antifreeze solution. Wipe down interior and refill tank 1/4 full with clean water.
  2. Reconnect your water heater’s plumbing. Check any sacrificial anodes and make sure the heater is securely mounted.
  3. Check your water pump’s electrical connections and make sure the pump is securely mounted. Check all hose connections and tighten any loose clamps.
  4. Open your in-line water filter, remove any standing antifreeze, and clean housing. Replace housing with filter element removed.
  5. Activate pump and open faucets one at a time. Once all faucets run clear, empty the water tank and refill with tank and hose cleaner. Let stand several hours, then pump the tank dry, replace the water filter element, and refill the tank with clean water.


Force 10 Marine,

Indel Webasto Marine USA,

Galley Maid Marine Products,


Raritan Engineering,


Whale Water Systems,


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