Is reverse osmosis water safe to drink on a boat?
We have a seawater reverse osmosis watermaker on our cruising yacht, feeding a 300-litre freshwater tank. Can we drink it straight from the galley tap, and do we need to add minerals or disinfect the tank?
Answer
Yes, reverse osmosis water is safe to drink on a boat when the watermaker works correctly and the freshwater tank, hoses and taps are clean. Check product-water salinity and the storage system first, because removing salt does not prevent contamination farther along the pipework.
Check before filling the tank
A seawater watermaker forces water through a reverse osmosis membrane under pressure. The membrane rejects most dissolved salts and forms a substantial barrier to microorganisms, but the whole installation still needs correct operation and maintenance.
Start with your unit's operating manual. Salinity limits, flushing arrangements and restart procedures vary between makes and model years. Spectra, Schenker and Dometic Sea Xchange installations may handle these jobs differently.
- Choose clean seawater. Avoid making water in marinas, near sewage outlets, in fuel slicks or where you suspect chemical contamination. An RO membrane does not guarantee protection against every dissolved chemical.
- Check the inlet strainer and prefilters. Restricted flow can reduce output and upset operating conditions. Fit the filter grades specified by the manufacturer.
- Divert the initial product water. Let the machine stabilise and confirm acceptable salinity before directing water into the tank.
- Check the rejection system. Where fitted, the salinity sensor and three-way diversion valve should automatically send unacceptable water overboard.
A handheld total dissolved solids meter gives a useful cross-check against the installed display. Use the maker's acceptance limit. A low TDS reading measures dissolved material; it cannot confirm that bacteria or chemical pollutants are absent.
Check the tank and hoses
Good water can become contaminated in a dirty tank, an old hose or a poorly maintained filter housing. Check the tank inspection opening, filler-cap seal and vent. Look for sediment, slime, damaged hoses and places where dirty water can enter.
Clean water can remain usable in a well-maintained tank for a long time. There is no dependable rule that tank water becomes unsafe after a fixed number of days. Starting quality, temperature and system cleanliness all affect how long it keeps.
Disinfect the whole freshwater system annually, and again after known contamination or work that introduces dirt. Physically clean a visibly dirty tank first. Disinfectant cannot replace the removal of sludge and deposits.
- Use a product intended for potable-water systems and compatible with the tank material.
- Calculate the dose for the volume being treated, including connected pipework where relevant.
- Draw the treated water through every outlet so it reaches the hoses and taps.
- Observe the product's stated contact time, then drain and rinse as directed.