Watermaker primer

Coastal sailors can usually carry enough freshwater to meet their daily needs. But if you sail in deep waters you may find that water must be rationed or used sparingly in order to make it last the trip &mdash that is, unless you have a watermaker. With a watermaker you can make fresh water anytime provided you have enough power. Watermakers are available for boats as small as 24 feet (although you'd probably not take a 24 footer across an ocean), giving mariners a freedom never before enjoyed.

How do you pick the right size watermaker for your boat? First, you need to determine how much water you use over the course of your voyages. For example, suppose you routinely empty an 80-gallon tank every weekend. You know that you use at least 80 gallons in two days, but how much more would you use with a reverse osmosis watermaker onboard? Typically, water use rises as the crew gets used to having almost unlimited water available. If you currently use about 80 gallons on a weekend, estimate that your water usage will increase by 50 percent with a watermaker. This must be taken into account when determining your water needs.

If you want to figure the amount you need exactly, you should estimate how much water you use for drinking, showering, shaving, washing dishes, and cooking in one 24-hour period. (Tip: you can do this at home simply by keeping a journal.) You can figure that most low-flow showerheads use at least a gallon per minute. If you have a washing machine on the boat, add its capacity into your total. Then divide this number by the total number of hours per day that you want your engine or generator to run because, in most cases, the engine or generator is required to power the watermaker. This will give you the number of gallons per hour output that you require. All you need to do now is match the number of gallons to your boat's voltage supply and figure the cost. You should also check to see that your generator or main engine alternator can handle the additional power. You might also check to see that you carry enough fuel to run your generator or main engine regularly to use the watermaker.

Having found the right size watermaker for your boat, the next step is to make sure that it can fit in the space available for it and that it is not too heavy. This may require making templates and offering them up to the space. You must also figure out where your water intake and exhaust will be. Make sure that the seawater intakes are well forward of any bilge, engine room, or head discharges.

Running times

If you intend to run your watermaker every few days, you should get one with a reverse flushing feature so that you can clean the membrane after making water. If you do not flush the membrane with freshwater after using it, and you leave it for a few days, it is likely to foul.

If you run a watermaker constantly, as you might on a powerboat, you can use a smaller system and may not need to have the back-flushing feature. However, if you do run the system constantly, you will need tanks large enough to hold all the water you make.

Ease of servicing must be considered when buying a watermaker. All watermakers need servicing, and that means that you need to have easy access to them. Some units have electronic displays that tell you when service is required. This readout indicates whether the pre-filters need cleaning, whether the oil in the high-pressure pumps needs changing, and most importantly, when the membrane needs to be cleaned. On other models, you must record how long the unit has been in use and service it accordingly.

There are several other points you should consider when looking for a watermaker. First, order the unit with an oil/water separator and a booster pump. An oil/water separator keeps oil away from the membrane. If oil gets on the membrane, the membrane will deteriorate and let saltwater through. Second, make sure the pump is self-cleaning to ensure that water stays pure. Some units flush their systems regularly to keep everything clean. Third, make sure the membranes are cleaned regularly. A dirty membrane makes the job harder and produces less water. Finally, if you intend on sailing to foreign ports, make sure that parts for your watermaker can be obtained worldwide.

If you want to make sure that your freshwater stays pure, there are several additional steps you can take. First, install an ultraviolet sterilizer and carbon filter in the water system so that all water goes through them before going to your faucet. Next, make sure that your boat's water supply is divided into at least two tanks. That way, if one tank is contaminated, a second tank is available. For this same reason, the watermaker unit should have an automatic diverter valve. Then, if contaminated water gets through the membrane, it will automatically be directed over the side.

How much power?

The next question is one of power availability. Emergency watermakers use a hand pump to produce freshwater, but they only make a few pints per day. In fact, you might sweat out more water than you can make with an emergency watermaker &mdash although you may have little choice in a survival situation.

Most onboard watermakers run on 12, 24, 110, or 220 volts. The voltage of the unit is not so important as the amperage draw. Some units draw up to 27 amps to make a gallon of water. If you run a 12-volt unit from a 60-ampere-hour battery, you can run the battery flat in under two hours and get less than two gallons of water. For this reason it is best to use either a generator (or a large alternator on the main engine) to drive the watermaker.

Having a watermaker onboard can free you from the constraints imposed by finding water in every port. It can also reduce the risk of inadvertently filling your tanks with contaminated water. But the drawback is that your watermaker system will usually require an additional generator or large alternator, and it will need maintenance to keep everything shipshape. On a long voyage, though, being able to take a shower at the end of a swatch is a morale boost that makes having a watermaker very worthwhile.

Roger Marshall is a sailor, designer and freelance writer who has written for a variety of publications. He lives in Jamestown, R.I.

Watermaker case study

I opted for a small watermaker that produces about seven to 10 gallons per hour, which is more than ample for my needs, provided I go to sea often enough to run the thing without taking in harbor water, and provided I am not spending a lot of time in the tropics. Mine runs on 12-volt DC power off the ship's batteries. This means I operate it only at sea and only when the batteries are being charged by either the generator or the engine's alternator. But it also means I don't have to have the inverter on or use shore power to operate it. I dedicated a separate 35-gallon tank for the product water with gravity feed from there into the two main 50-gallon water tanks. That way I know the water in the first tank is chlorine-free and can be safely used for back-flushing the membranes on a weekly basis.

I do have a fresh-water shower on the boat, but we don't use it very often, at least not in high latitudes. The real beauty of having a watermaker is the freedom from ever having to take on city water, especially in ports around the world where the quality of the water may be less than ideal. The product water from the watermaker is essentially the same as distilled water. It contains no salts, no particulates, and no bacteria or viruses. If one is going on a long passage, it is obviously prudent to start with full water tanks and to ration usage on the assumption the watermaker may stop functioning for any of a variety of reasons. But as long as it's working, it is a great comfort to the off-shore sailor to have a way of replenishing the supply of fresh water as it is being consumed.

The only down side (other than the expense) is the need to maintain the device. Once put in operation, the membranes must be kept moist. So it needs to be run every couple of days. In addition, it needs to be back-flushed with chlorine-free water once a week. Most models can be set up to do this automatically. If the system is not going to be used or back-flushed regularly, the membranes have to be removed and placed in "pickling" solution to keep them healthy and free of bacteria. So it's one more system on board to worry about, but well worth the effort for those who voyage extensively.

Boat name: Cielita
Make and length: J Boats, 46 feet
Total water tank capacity: 135 gallons in two 50-gallon main tanks and one 35-gallon tank dedicated to the product water
Watermaker brand and model: Sea Recovery, Ultra Whisper (12v)
Watermaker maximum output capacity in gallons per hour: 10
Your typical watermaker output per day: 10 to 20 gallons as needed

Ned Cabot

Watermaker manufacturers

This list provides information about a number of manufacturers of reverse osmosis watermakers.

FCI Watermakers
FCI Watermakers range from 25 gallons per hour up to 400 gallons per hour and so can be used on smaller vessels all the way up to superyachts. The UROC – universal reverse osmosis controller allows operation from remote locations at the push of a button.

FCI Watermakers, Inc.
221 West Dyer Road
Santa Ana, CA 92707
Tel: (714) 850-0123  
Toll-free within the US:
Fax: (714) 850-0955
Web: www.filtrationconcepts.com
E-mail: info@fciwatermakers.com

HRO – Horizon Reverse Osmosis
HRO was among the first developers of reverse osmosis watermakers. It started to manufacture these units in 1975. The company makes a range of units that produce from 8 gallons per hour to 6,800 gallons per day.

Horizon Reverse Osmosis – USA
P.O. Box 5463
Carson, CA 90745-5288
Tel: (310) 631-6300
Toll-free within the US:
Fax: (310) 631-6395
Web: www.hrosystems.com
E-mail: sales@hrosystems.com

PUR hand-operated watermakers should be in the grab-bag of every boat going offshore. They require serious pumping to push the water through the membrane, but if you are stuck in a life raft a hand-operated unit can be a lifesaver. The PUR 06 requires 40 strokes per minute to produce 1 ounce of water every two minutes. The PUR 35, another hand-operated unit, requires 30 strokes per minute and makes 1.2 gallons per hour, although it would be hard to keep pumping for an hour. While the PUR hand-operated units can generate enough water to keep you alive, you would probably end up with muscles like Charles Atlas if you were in a life raft for many days.

PUR Recovery Engineering, Inc.
9300 North 75th Ave.
Minneapolis, MN 55428
Tel: (612) 315-5500
Toll-free within the US:
800-845-7873 x 5561
Fax: (612) 315-5503

Sea Recovery
Sea Recovery is probably one of the most well known names in reverse osmosis watermaking. The company offers many models. The units can supply water for boats from 25 feet long to megayachts, and the capacities range from 25 gallons per hour to 6,800 gallons per day for large yachts.

Sea Recovery – USA
P.O. Box 5288
Carson, CA 90745-5288
Tel: (310) 637-3400
Toll-free within the US:
Fax: (310) 637-3430
Web: www.searecovery.com
E-mail: stylesrcsales@searecovery.com


The Baltic line of watermakers ranges from 200 gallons per day to 1,800 gallons per day. The units use stainless steel piping and a titanium pump with a lifetime warranty.

Skimoil, Inc.
103 W. Weaver St. #209
Carrboro, NC 27510
Tel: (314) 579-9755
Fax: (314) 558-9253
Web: www.skimoil.com
E-mail: info@skimoil.com

Spectra uses what the manufacturer calls a patented Clark pump. The Clark pump is a pressure intensifier that uses two opposing cylinders and pistons that share a single rod. The pump works in both directions to force water through the membrane. This significantly lowers the power consumption of the unit to where, in some cases, it makes 8 gallons of water for 8 amps of power draw, one of the lowest power requirements you can find. Spectra watermakers also use a patented Z Guard system that puts 36,000 volts at a microamp through the incoming water to kill off bacteria and other ocean organisms. This system keeps the membrane cleaner and improves the quality of the freshwater.

Spectra Watermakers
20 Mariposa Rd.
San Rafael, CA 94901
Tel: (415) 526-2780
Fax: (415) 526-2787
Web: www.spectrawatermakers.com
E-mail: techsupport@spectrawatermakers.com

Village Marine Tec.

Village Marine Tec. has an honest claim to being the originator of the marine watermaker, and it still makes more than 50 percent of its own products. Village Marine uses titanium pump heads and offers a lifetime guarantee on its units. Village Marine watermakers come in a variety of sizes and styles, the smallest being the Little Wonder unit, which makes 150 gallons per day. The No Frills unit has an output of 200 to 1,200 gallons per day, while the Squirt has a 200 to 600 gallons per day capacity.

Village Marine Tec
2000 W 135th St.
Gardena, CA 90249
Tel: (310) 516-9911
Toll-free within the US:
Fax: (310) 538-3048
Web: www.villagemarine.com

Roger Marshall

Onboard water usage per day

The following are some water usage estimates. The actual amount of water you use will vary depending on how warm the weather is, your type of boat, the number of heads on board, your proximity to a marina, and other factors.

  • Showering and washing: Allow 3 to 8 gallons per day, per person, less if you don't shower aboard.
  • Drinking and cooking: Allow 4 to 6 gallons per day, per person.
  • Dish washing: Allow 4 to 6 gallons per day.
  • Hand-washing clothes: Allow 2 to 4 gallons per day, per person.

Points to consider:

1. If we assume that two people use 40 gallons of water a day, and we want to run the generator for two hours per day, we need a watermaker that can make 40/2 = 20 gallons per hour, or 480 gallons per day.

2. Reverse osmosis watermakers can make large amounts of water. The exact amount is determined by the size of the pump and the ram chambers, plus the temperature of the water and the state of the membrane. Most manufacturers list the amount of water made in gallons per day, assuming that your pumping system is operating for 24 hours a day. However, most sailors run their main engine or generator for only an hour or two per day, so the amount of water that is actually made will be a lot less than the manufacturer states.

3. Another way of looking at how large a watermaker you need is to consider the amount of water you currently carry on your boat. Based on a recent survey that I made of more than 100 boats, the weight of water carried on a voyaging sailboat is equal to about 5 to 7 percent of the displacement, while on a racing sailboat it equals about 2 to 4 percent. On boats that have a watermaker, however, the weight of water carried seldom exceeds 2 to 4 percent of the displacement, even on voyaging boats.

So by installing a watermaker, you can cut the amount of water you carry by about 50 percent. This means that if the watermaker weighs less than 50 percent of your boat's water tankage, you will increase the boat's performance because you will reduce overall weight. If a gallon of water weighs 8 pounds, then a 100-gallon tank will weigh around 840 pounds (including the weight of the tank). Therefore, if the watermaker you install weighs less than 400 pounds, you come out ahead.

4. If you install a watermaker purely to supplement your water supply, you should also consider how you are going to store the water. There is no point to buying a 400-gallon per day watermaker if you only have a 60-gallon freshwater tank to store the water in.

Roger Marshall

Watermaker case study

There are several things we like about our watermaker. First, no transporting jerry cans to and from the boat in the dingy. Second, we make water everywhere. Even when we tie up at a marina, we only use dock water for washing the boat. Filters are cleaned and changed every 12 run hours in a dirty harbor or marina and every 24 run hours in clean anchorages. Third, we tried to make Andiamo as much a 12-volt boat as possible. Our watermaker, with the twin 12-volt pumps, draws 9 amps per pump. We do not need to run our engine to produce water, ever! We added battery capacity (see ON #130, May/June 2003) and our six solar panels supply all the energy we normally need. Lastly, we do not need to get water in areas where there's a lack of water. Our cruising grounds are primarily the west coast of Mexico and the Sea of Cortez, with a nine month sail to French Polynesia and back a couple of years ago. There was a severe water shortage when we were in the Tuamotus. The Polynesians are very generous people and would have given us water if we needed it, but it would have been a hardship for them.

There are also a few things we don't like. The first thing is the low capacity of our watermaker. The best we have ever seen was about 13 gph and that was in the cold waters of the northwest. In warm waters, the performance is lower and we only get about 10 to 11 gph with both pumps running. Another problem is the pumps themselves. If both pumps are run at the same time, they "fight" each other and the pump life is cut in half. This is a basic engineering issue and I would think that Spectra would have supplied pumps and/or new pump heads on an extended warranty basis or at reduced cost. Our model is no longer in production.

Boat name: Andiamo
Make and length: Wauquiez Pretorien 35
Total water tank capacity: 33 gallons (we converted a second 33 gallon tank to diesel)
Watermaker brand and model: Spectra Santa Cruz
Watermaker maximum output capacity in gallons per hour: 10
Your typical watermaker output per day: 25 to 30 gallons every third day

John and Lisa Caruso

Watermaker Case Study

We're particularly pleased to be asked about our 19-year-old watermaker, Grendel the Groaner. Already appreciative of its simple virtues when we purchased Carricklee 17 years ago, we moved Grendel with us from our previous boat. Like an old friend, this 19-year-old PowerSurvivor 35 has been steadfast and reliable, never once failing to come to life when we've turned on the switch, and we know how to get along with it. We have resisted the temptation to replace Grendel with a newer model simply because it has been so dependable and easy to operate.

Before we leave a harbor, we fill our two belowdecks water tanks as well as three six-gallon jugs we carry on deck in case of contamination in the tanks or watermaker failure, neither of which has ever occurred. Because we use water sparingly at all times, we usually run the watermaker at most five hours a day, enough to supply us with six gallons, the amount we use on a normal day if we're alone aboard Carricklee.

The upkeep on our primitive watermaker has been minimal. When we are out cruising, we generally run the watermaker every day or two. When we anticipate not using the watermaker for five or more days, we pickle it according to the manufacturer's instructions. Over these 19 years &mdash 12 years, and 50,000 miles, of those on this current cruise &mdash we've replaced the O-rings twice because the unit had begun to leak. Otherwise, it has not been disassembled. We clean the membrane as recommended in the manual and, no doubt as a result, are still using that original membrane. We keep six or more pre-filters in reserve, but haven't disposed of many used pre-filters. Instead, we normally remove the fouled one once a week and clean it by trailing it in saltwater as we're under way.

Boat name: Carricklee
Make and length: Hardin 45 ketch
Total water tank capacity: 180 gallons
Watermaker brand and model: PowerSurvivor 35 (now Katadyn)
Watermaker maximum output capacity in gallons per hour: 1.25
Your typical watermaker output per day: 6 gallons

Bob and Carolyn Mehaffy

By Ocean Navigator