1. Measure an actual water budget
Begin with a daily record of water aboard, additions and uses: drinking, cooking, washing, dishes, flushing and losses. The methods proposed here organise your records; they are not a public-health sizing standard. Identify an approximate tank gauge as approximate rather than silently treating it as an exact measurement.
The basic relationship is: closing stock = opening stock + additions − consumption − losses. Observe several representative days before drawing conclusions. Separate potable water from water reserved for other purposes instead of combining them into a misleading endurance total. Record crew numbers, heat, activities and changes in habits that help explain differences between days.
References for this section : OMS / WHO — Guide to ship sanitation, chapitre Water, 3e édition, 2011
2. Calculate with no production first
WHO highlights the need to retain stored water while onboard production is unavailable for maintenance or repair. Its guide concerns ship sanitation; it does not provide a universal number of days suitable for every sailing yacht.
A hypothetical whole-boat example: 180 usable litres, of which 60 are retained as a separate reserve, and observed consumption of 30 litres per day give (180 − 60) / 30 = 4 days before using that reserve. This arithmetic does not establish human water requirements. Repeat the exercise for a longer passage and failed production. Choose a replenishment decision point before reaching your chosen threshold, allowing for practical access to a safe supply.
References for this section : OMS / WHO — Guide to ship sanitation, chapitre Water, 3e édition, 2011
3. Separate rated flow from water actually available
Rainman states that production varies with factors including water temperature and salinity. Performance in one set of conditions is therefore not a promise everywhere. Use the particular model’s documentation and measurements aboard.
Keep a record for each run: duration, volume admitted to the tanks, prefilter condition, supply conditions and faults. The net volume must account for water used in flushing: Rainman describes an automatic system supplied from the freshwater tank. A run can complete without every displayed litre remaining available for living aboard. Avoid counting one production run twice, first as machine output and then again as a separate tank addition.
References for this section : Rainman — Electric watermaker operations guide · Rainman — Watermaker autoflush system
4. Connect water production to energy demand
Equipment range and power supply vary by model; Schenker documentation distinguishes several configurations. Before choosing a running period, identify the exact machine, associated pumps and any inverter supplying them.
A deliberately invented calculation example: a system drawing 300 W for two hours uses 600 Wh. If it actually delivers 100 litres during that run, the observed ratio is 6 Wh per litre, before any loads excluded from the measurement. Use this ratio to compare your own operating cycles. It does not describe any product cited here. Add the load to the electrical budget and examine what happens if expected charging does not arrive.
References for this section : Schenker — Zen watermakers and model documentation
5. Maintain the installed model, not a generic recipe
Spectra directs owners to the manual for commissioning and compatible preservation chemicals. Rainman warns that residual chlorine in tank water can damage membranes in its installations when unsuitable water is used for flushing.
Keep a sheet with model, serial number, manual version, filter references, due dates and the last intervention. Distinguish routine flushing, prolonged storage, cleaning and recommissioning: these are different operations. Do not swap a chemical between brands because its name looks similar. Frequencies, quantities and procedures must come from the matching manual; this dossier provides no disinfectant or preservation-chemical dose. Check that instructions match installed options as well as the main machine.
References for this section : Spectra Watermakers — Support FAQ and long-term care · Spectra Watermakers — Manuals and downloads · Rainman — Watermaker installation guidelines, version 2.0
6. Protect stored water and separate the backup
CDC guidance recommends suitable, closed containers protected from recontamination, without reusing containers previously used for toxic substances. This general storage advice does not certify a boat tank’s sanitary condition.
Trace the water route from filling point to tap. Identify tanks, valves and shared pipework. Two permanently connected tanks may share a leak or contamination; their number alone does not establish independent reserves. Prepare a clearly identified backup stock accessible without the main pump. Choose its volume and renewal arrangements for the voyage and applicable health guidance, without subtracting the crew’s essential needs. Make sure another person can locate and access it if the usual water-system operator is unavailable.
References for this section : CDC — Safe water storage
7. Recognise the limits of a reading
USGS describes conductivity as an indicator associated with dissolved solids. A salinity or TDS reading therefore tells you about one aspect of water; it is not a full microbiological analysis or a general guarantee of safe drinking water.
If equipment fails, water becomes suspect or maintenance history is uncertain, isolate production as instructed and use a safe reserve. Do not taste suspect water to decide whether it is safe. Record readings and symptoms, then seek help from the manufacturer or a competent technician and, for sanitary quality, the relevant authority or laboratory. Before departure, decide who maintains the record and what action follows a sustained loss of production.
References for this section : USGS — Chloride, salinity and dissolved solids · Spectra Watermakers — Manuals and downloads
Plan the passage around measured reserves and a no-production scenario; treat the watermaker as a monitored contribution, never a guaranteed supply.
Your practical checklist
Sources & documents
- Rainman — Electric watermaker operations guide
Accessed 2026-11-02 - Rainman — Watermaker autoflush system
Accessed 2026-11-02 - Rainman — Watermaker installation guidelines, version 2.0
Accessed 2026-11-02 - Spectra Watermakers — Support FAQ and long-term care
Accessed 2026-11-02 - Spectra Watermakers — Manuals and downloads
Accessed 2026-11-02 - Schenker — Zen watermakers and model documentation
Accessed 2026-11-02 - OMS / WHO — Guide to ship sanitation, chapitre Water, 3e édition, 2011
Accessed 2026-11-02 - CDC — Safe water storage
Accessed 2026-11-02 - USGS — Chloride, salinity and dissolved solids
Accessed 2026-11-02
