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Solved problems · Plumbing · Crew answer

Why does my boat's fresh water smell or taste bad?

Musty, sulfur or rotten-egg tasting water usually means bacteria or biofilm in the tank, hoses or water heater. Here's how to sanitize the system with diluted bleach and flush it.

Symptom

Tap water smells musty, swampy or like rotten eggs, tastes off, or looks cloudy, often after the boat has sat or after filling from a new source.

Likely cause

Warm, stagnant water lets bacteria and biofilm grow in tanks, hoses and the water heater. Sulfur smells often come from bacteria that thrive in low-oxygen water, and a rotten-egg smell only in the hot water can come from the water heater's anode reacting with the water. A clogged tank vent, old hoses and filters that are past due add to it.

Stop now if

Anyone aboard gets sick after drinking the water. Stop drinking it and use bottled water until the system is cleaned. Never mix bleach with other cleaners, and ventilate the boat while you work.

The fix, in short

  1. Drain the tank and water heater. Empty the tank and, with the heater's power off and the water cool, drain the water heater too.

  2. Mix the right bleach dose. Practical Sailor gives about 0.13 ounces of plain, unscented household bleach per gallon of tank capacity, or 1 milliliter per liter. Premix it in a gallon of water before adding it to the tank.

  3. Fill and run every tap. Fill the tank with potable water, then run each hot and cold tap, the shower and any deck wash until you smell chlorine. Let it stand for the time your cleaning instructions recommend.

  4. Drain and flush until clear. Drain everything, refill with fresh water and flush again. Repeat until the bleach smell is gone.

  5. Replace filters and check the vent. Replace carbon or sediment filters after sanitizing, and make sure the tank vent screen and hose are clear.

  6. Keep it fresh. Use and refill water regularly, and repeat the sanitizing when the boat has sat or water starts to smell.

Written by Sailor Cruiser crew. General guidance, not an inspection of your boat.

Equipment involved

  • Fresh water: Water tanks, vent, hoses, pressure pump, filters and water heater

Related guides

Sources

Background reading we checked while writing this answer. The wording above is our own.

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