BoatTanks

Only if the tank is made from a WRAS-approved material rated for potable use — check this before fitting, as not all flexible tanks are food-grade. Tanks intended for fresh drinking water should be free from taste or odour transfer and easy to sanitise. If you're storing water for washing or ballast only, a non-potable grade is perfectly adequate.

Measure the void you're filling — under a berth, in a locker, or a hull cavity — in its collapsed and fully expanded state, as flexible tanks need room to bulge once filled. Capacities typically run from 40 to 300 litres, so weigh this against your crew size, trip length and the vessel's payload limits. It's worth choosing a shape that matches the compartment rather than the largest tank that will technically fit, as overfilled bladders can strain fixing points.

Most bladder tanks come with reinforced eyelets or webbing loops at the corners so they can be strapped or lashed down inside a locker or compartment. They should be secured on all sides to stop movement in rough water, as an unsecured tank can chafe against fittings or block bilges if it shifts. Fit inlet, outlet and vent hose connections before final tightening, since access gets tighter once the tank is strapped in place.

Reinforced PVC is generally lighter and more cost-effective, making it popular for day boats and shorter trips. Polyurethane offers better abrasion and puncture resistance along with greater flexibility in cold conditions, which suits long-distance or offshore sailing where the tank will flex repeatedly. Both are durable when properly installed, so the choice usually comes down to how hard the tank will be worked and the conditions expected.

No — tanks are manufactured and lined for a specific liquid, and fuel, waste and fresh water each need different material compatibility and fittings. Using a fresh water tank for diesel or grey water risks contamination and can degrade the tank lining. Always check the intended use stated by the manufacturer before installation.

Drain fully and flush with a mild sterilising solution before laying up, then rinse thoroughly to remove any residue that could taint water next season. Store the tank empty, loosely folded and in a dry location away from sharp edges or rodents, as flexible materials can crack if creased tightly for long periods. Check fittings and seams for wear before refitting in spring.