Why is the water from my boat's osmosis system cloudy?

Cloudy water from a boat's reverse-osmosis watermaker often contains tiny air bubbles, especially after a filter change, freshwater flush or restart. Check a fresh sample in a clear glass: water that clears from the bottom upwards usually contains air, while persistent haze, sediment or an unusual smell needs investigation before you fill the tank.

Try the clear-glass test

Following the operating instructions, take a sample from the watermaker's designated product-water sampling outlet before it enters the tank. Use a clean, clear glass against a dark background and leave it undisturbed for five minutes.

• Clears from the bottom upwards: fine bubbles are rising and escaping, which strongly suggests entrained air.
• Particles settle on the bottom: suspect sediment, filter debris or contamination in the sampling hose or downstream plumbing.
• Haze remains throughout: investigate contamination, mineral precipitation or residues from preservation or cleaning.

Compare the sample with a glass from the galley cold tap. Clear water at the watermaker but cloudy water at the tap points to the tank, domestic pressure pump, aerator or drinking-water filter. If only hot water is affected, investigate the calorifier and hot-water plumbing.

Until persistent cloudiness or an unusual smell is explained, divert production away from the drinking-water tank and use a known safe supply.

Check intake and filter housings

A newly opened prefilter housing can hold air, and restarting after maintenance may briefly produce bubbles. Purge the system using its normal start-up procedure and watch for the cloudiness to diminish.

If bubbles keep returning, check the seawater feed side:

1. Check that the intake seacock is fully open and the seawater strainer is clear.
2. Check strainer-lid seals and prefilter-bowl O-rings for dirt, twisting or damage.
3. Inspect suction-hose connections and clamps. A joint can draw air under suction without visibly leaking water.
4. Check for a restricted intake or exhausted prefilters, especially if feed pressure has fallen or the pump sounds different.

Stop the equipment and close the intake seacock before opening seawater strainers or filter housings. Reassemble, reopen the seacock and check for leaks before running. Use only the manufacturer's specified seal lubricant and avoid overtightening plastic bowls.

Check filters and recent servicing

Start with whatever changed just before the haze appeared: replacement cartridges, recommissioning after storage, membrane cleaning or work on the freshwater plumbing. Black specks after changing a downstream carbon cartridge suggest carbon fines. Flush that cartridge according to its instructions.