Potable Water Sources While at Sea

Sondra W. Lee, P.E. President, FWEA

People occasionally ask how drinking water is supplied on boats. When it comes to potable water sources, a boat at sea can be compared to traveling by recreational vehicle, backpacking, or living in a remote location: it’s possible, but takes a little bit of planning and time.

There are a few options to ensure you have safe drinking water while traveling. These may vary depending upon where your travels take you.

Bottled Water

For short trips, the simplest option may be to fill your own water bottles and bring them along. A weekend or weeklong trip may require filling or purchasing jugs of water. This was the method I used for the first few years on my 32-foot sailboat, when our longest trip lasted about three nights. Since a leaking jug can quickly become a problem beyond just having to wipe up water, it’s prudent to bring an extra jug.

Onboard Tanks

That 32-foot sailboat had 50-gallon tanks of water storage onboard, but for those first years, I was not ready to drink the water from them. Instead, water from the tanks was just used for washing dishes and for a freshwater rinse after bathing in the sea, while drinking and cooking water was supplied by the jugs we brought onboard.

Utility-Supplied Water

We had the luxury of filling those tanks with utility-supplied water at a dock at our house, so we knew the water supply was good, but we were uncomfortable with seeing floating objects in the water no matter how many times I flushed and bleached the tanks. After a couple of years, we added a filter to the faucet and began drinking the utility-supplied water from the tanks. With this new setup, we ventured out to a longer trip of six days with no issue to anyone onboard.

Our current 40-foot sailboat is not kept at our home so utility-supplied water is provided at marinas, with varying levels of maintenance and care. I’ve seen a broken water pipe sitting in marina water waiting to be repaired, and I’m not so sure that the facility disinfected the line before putting it back into service. In this case, we provided extra filtration through the water system, starting with a portable filter as the water enters the tanks.

Stormwater

Some sailors rely on rainwater to supplement their water tankage. They will set up their sails and shade covers to funnel water into jugs or direct the water into their onboard tanks. Others will open the deck caps to the water tanks and let the water directly drain into the tanks. This is an old method of water supply at sea; however, being at the mercy of rain (and a dose of salt in the water) had me looking for better methods of long-term water supply.

Water Maker

With luck, the boat we currently own came with a water maker and 175 gallons of water storage used regularly by the former owners during their nine years of cruising. The water maker is a small reverse osmosis membrane system. It contains a low-pressure pump that pulls water from the sea and into a prefilter prior to a high-pressure pump that passes the water through the membrane. Brine from the process goes overboard as reject water and acceptable water is sent to the onboard tanks.

As a side note, an extra house filter is placed on a faucet dedicated to drinking and cooking purposes as it exits the tanks.

The U.S. Environmental Protection Agency allows a total dissolved solids level up to 500 milligrams per liter for potable water. The water maker removes pathogens and reduces the seawater salinity from about 35,000 to 200 milligrams per liter. A meter is used to ensure that it reads 300 milligrams per liter or less, but we prefer it to be at 200 before diverting the water to the storage tanks.

There are some maintenance considerations with a water maker onboard. For one, it must be used frequently, or pickled. Water needs to be made every five days or undergo a freshwater flush. During the freshwater flush, a carbon filter is used to ensure that chlorine from a utility-supplied water source is not sent to the membrane.

Location is an important factor in deciding when to use the water maker; it’s recommended to be away from shore in waters without known issues. For example, a water maker should never be used while at a marina, and probably should not be used during red tide conditions.

I can recall the first time I drank water made onboard. During a chilly morning sailing on Sarasota Bay my husband stepped down below to make the first batch of water on our new-to-us boat. He had been down below for quite some time, while I thoroughly enjoyed maneuvering across the bay. About an hour later he popped up and handed me a glass of water, which I absent-mindedly took from him and drank from it. When he asked how the water tasted with a big grin on his face, I became alarmed and asked, “Is this from the water maker?” and “Did you test it?” His response was laughter since the answer was yes to both questions. Since then, I have consumed water from various bays with no issue and love the freedom a water maker has brought to our travels.

Extra Appreciation for UtilitySupplied Potable Water

Like many people, I at times take my potable water supply for granted. Then, when sailing or backpacking, I am quickly reminded how fortunate it is to have abundant, safe, and reliable water provided by a local utility. S