On our first boat, on which we cruised around the Caribbean for 15 years and raised our children, I installed a noisy fresh water pump under the saloon sole where it could be clearly heard all over the boat whenever it was running. We were effectively able to enforce water discipline. To this day, all members of the family never leave a faucet running!
We had other water conservation measures, which some guests found to be rather repulsive (notably using the dishwater until it was pretty disgusting and obliging anyone who took a shower to tromp up and down on the laundry). We had the decks organized such that in a squall we could flush them and then divert the rainwater to the water tanks. We never came close to running out of water, but we had to engage in active water management.
The combination of a near-silent water pump and the watermaker on the last boat encouraged a certain degree of reckless water use. With the family, old habits die hard, but guests are another matter. Theyâ€™ll wallow in the shower for extended periods, and run the faucet while brushing their teeth or washing a teacup. I find it hard to take (and to keep my mouth shut) but itâ€™s really not a problem. Itâ€™s all part and parcel of a cruising lifestyle that has changed dramatically over the past 20 years.
Installing a watermaker
Watermakers can be bought as an integrated unit mounted on a common base plate (a â€œcompactâ€� unit) or as component parts, which are mounted individually in the boat (a â€œmodularâ€� unit). There is generally little difference in the purchase price, although there will often be a significant difference in the installation cost because of the added work required by the modular units. The choice of which to use will be driven by the available spaces on the boat, bearing in mind:
â€¢ The raw water intake must be as low in the boat as possible (in order to ensure that the system receives a constant supply of water with no air entering the feed line). It must be located well away from toilet discharges, and sink, shower and bilge pump drains. Flat hull inlets should be avoided because they can cause a vacuum; a forward facing scoop is recommended. The through-hull inlet should be dedicated to the watermaker alone to avoid the risk of air entering from another system, and to ensure adequate flow to the watermaker.
â€¢ Hose runs should be kept as short as possible, with as few restrictions (e.g. bends) as possible, in order to minimize friction in the system. This is especially important on the low-energy systems, where every extra foot of hose or additional bend absorbs pump energy and lowers performance.
â€¢ It is a good idea to place the through-hull for the brine discharge above the waterline so that the discharge can be monitored.
â€¢ All components, especially filters, need to be readily accessible.
â€¢ Some salt water will inevitably be lost when changing filters so the filter housings need to be placed where the water will not drip on sensitive equipment.
â€¢ The high-pressure circuits may develop a drip. All connections need to be located where they also will not drip on sensitive equipment (at any angle of heel).
â€¢ Traditional watermakers are noisier than the low-energy models: they need to be located where they will not disturb the crew.
Following installation, it is an excellent idea to log as much benchmark data on the performance of the unit as can be measured with the available instrumentation. This data will provide valuable reference points for future monitoring and troubleshooting (in particular, giving early warning of filter and membrane fouling). It should include such things as:
â€¢ The source water (sea water) temperature.
â€¢ The feed water pressure (if there is a booster pump) or vacuum (if there is no booster pump) upstream of the filters (on the inlet side of the main pump).
â€¢ The operating pressure on the system (at the membrane housing).
â€¢ The product water flow rate (if no gauge is available, this can be measured by diverting the flow to a bucket and timing how long it takes to collect a measured amount).
â€¢ The salinity of the product water (if there is a salinity meter).
â€¢ The brine flow rate (this can be measured by holding a bucket below the discharge through-hull and timing how long it takes to collect a measured amount).
â€¢ The amp draw on a DC system.
Filter and membrane care are the two principal maintenance issues with watermakers. In addition, most high-pressure pumps, and some booster pumps, have an oil-filled sump that needs checking from time to time.
The addition of some kind of a monitoring device (such as a pressure gauge on the suction side of the main pump) that will warn when filters start to plug is recommended; more sophisticated watermakers also have an automatic shut-down circuit that will not allow the watermaker to be run with plugged filters.
Raw water strainers are cleaned as with an engine raw water strainer â€” most have a removable basket that is washed out in seawater.
Additional filtration generally consists of some kind of a removable pleated filter. These can often be cleaned by careful flushing of the filter surface. Each time it is hosed off will yield approximately an additional 50-percent life expectancy (e.g., if the new filter runs 100 hours, after the first hosing it will go another 50 hours, and after the second another 25 hours, etc.). At the first sign of damage, the filter must be discarded (some manufacturers recommend to clean no more than once and then discard).
Depending on how the watermaker is used, membrane care can be the major part of the needed maintenance. The extent of the work involved varies markedly from unit to unit, principally as a function of the quality of the source water filtration, regularity of use, whether or not there is an automatic flushing circuit, and the extent to which membrane maintenance is rendered unecessary by a Z-Guard or Z-Brane unit.
Flushing a membrane
As noted previously, if a membrane is left unused for more than a week, it will be susceptible to bacterial fouling. The best way to minimize watermaker maintenance is to use it often: in other words, do not fill the tanks and then shut the watermaker down for two weeks; instead, top off the tanks at least every three days. If the unit is to be left unused for more than a week without Z-Brane protection, it either needs to be put into storage mode or else flushed with fresh water at least once a week.
Note that long-distance passagemakers confronted with an approaching storm may find it advantageous to top off the tanks before the storm hits. This way there will be plenty of water on board, and the system will not need to be run, flushed or maintained in any way for several days.
Typically, the water used for flushing (somewhere between five and seven gallons) is drawn from the boatâ€™s water tanks. However, traces of chlorine will do permanent damage to membranes. For this reason, some installations include a separate tank into which product water is diverted and held for flushing purposes, while others include an activated charcoal filter between the water tanks and the flushing circuit. The charcoal filter removes any traces of chlorine. Note that once wetted, charcoal filters only last about six months.
Bare-bones systems have to be flushed manually, which is done by switching a couple of valves on the inlet and discharge sides of the watermaker and then turning it on. Sophisticated systems have automatic flushing controls powering solenoid-operated valves. The flush interval can be set by the user. This enables a watermaker to be left idle for some time without the need to pickle the membrane (so long as the unit does not run out of flushing water).
On some units, the flushing water also passes through the feed pump, while on others it does not, which leaves salt water standing in the pump. If the pump is made of plastic (e.g. the Shurflo pump used by Spectra and others) this is not a problem, but if it is made of stainless steel it may lead to corrosion.
Pickling a membrane
Special biocides are used for pickling a membrane. These are mixed with product water and then pumped through the system, leaving the membrane cylinder full of the biocide solution. When it comes time to put the unit back in service, the biocide is flushed out by running the unit in an unpressurized state (to achieve maximum flow through it, with no product water production) for some time (generally 15 to 20 minutes) before restoring pressure and production. The initial product water will still be high in dissolved solids, and so must be discharged overboard via a bypass line (this is the case any time a watermaker is first started). On cheaper units, this is done manually; on more sophisticated units, a salinity meter controls an automated bypass circuit.
Note that some watermakers (notably Spectra) include parts that will be degraded by some pickling agents. It is essential to use only the pickling agent recommended by the manufacturer.
Winterizing takes the form of pickling the membrane (it must never be left dry), draining the filters and the rest of the plumbing (filters should not be left wet) and, in some cases, adding potable antifreeze (propylene glycol, such as is sold for winterizing RVs and caravans) to the high-pressure pump (the low-energy pumps, in particular, can trap water that is hard to drain out; this can crack the pump in a hard freeze). Spectra also recommends pickling the membrane with propylene glycol, and in fact suggests this for pickling in general, because â€œthis seems to do less damage to the membranes than other storage compounds.â€�
In general, it is best to backflush the system every week, if this can be done, rather than pickle it during a relatively short-term lay-up.
Cleaning a membrane
Over time, a membrane inevitably becomes fouled. A watermaker will exhibit higher than normal pressures and lower than normal product water flow rates. However, before assuming the membrane is to blame, check the feed salinity, feed temperature, operating pressures and filters. Also, check the operating voltage (DC or AC) at the pump under load. DC systems, in particular, will be significantly affected by low voltage.
Membranes need cleaning on average once every two years (membrane life, on average, is five years). There are two types of membrane cleaner â€” alkali and acid. The alkali is most effective on biofouling and is generally used first (some firms recommend using the acid first). The acid is effective on mineral fouling (e.g., calcium), but is generally only used if the alkali fails to restore product water flow rates.
To clean a membrane, it is first flushed with clean water and then the alkali solution is mixed with the clean water in a bucket (preferably hot water to improve the performance of the cleaning agents). The unit is depressurized, and the suction, product water and discharge lines diverted into the bucket. The unit is run for an hour or so to circulate the solution through the membrane, then allowed to rest for an hour or so, and run again for 15 minutes or so.
After this, the system is put back into service, unpressurized and run for 15 minutes or so to clear out the cleaning solution before being returned to regular service. Once again, the initial product water will need to be discharged overboard, either manually or automatically.
If performance is still poor, the same procedure is repeated with the acid cleaning solution. Cleaning membranes is hard on them and something of a crapshoot. It should only be done when other measures do not restore output or operating pressures.
When operated with properly filtered source water, traditional watermaker high-pressure pumps will need the valves and seals replaced approximately every 2,000 hours of use. The manufacturers provide rebuild kits and instructions. Booster pumps and the feed pumps on the low-energy systems will also need an overhaul at similar intervals of use. Additionally, those pumps that have an oil-filled crankcase need an oil change every 500 hours.