PS Advisor: Acid Cleaning Potable Water Systems


You won’t find recommendations or articles from health authorities about sanitizing plumbing or drinking water equipment with vinegar because it isn’t very effective. Some bacteria and fungi like an acid pH, which is obvious since they are used to make vinegar. A moderately low pH may inhibit their activity, but it won’t kill them and as soon as the pH becomes more pleasant for them, they leap back to life.

The same goes with baking soda; a pH of greater than 10 is required for effective sanitizing and will kill all microorganisms, but baking soda solutions have a pH of 8.4 or less. Like vinegar, it will reduce their numbers, but not dramatically. But this does not mean that vinegar, citric acid and other acid cleaners do not have a place in restoring neglected potable water systems.

We’ve recommended borax-based formulations for killing and preventing the return of mildew. Some of the effectiveness derives from high pH (mildew prefers low pH) and some from its natural antibiotic activity. But borax is too toxic to use around drinking water, so scratch it off your list. It is safe for surface cleaning, fabric treatment, and skin contact, but it is forbidden in potable water systems.

Hydrogen peroxide and peracetic acid are effective sanitizing agents, often used in food processing industries, but they are highly toxic and must be thoroughly rinsed from the system prior to use. We think they are too hazardous for DIY use at the required concentrations without training.

We have recommended bleach for sanitizing potable water systems—it is the ANSI-recommended method. But it is not effective on plumbing with significant scale or biofilm build-up, because no sanitizing agent can quickly penetrate thick deposits. For this, a good acid cleaning can help.

We’ve studied many acid cleaners for their ability to remove scale, dirt, and oxidation from metals and hoses. Muratic acid, lactic acid, and phosphoric acid are highly effective, but we would rather not use these in potable water systems, because of safety issues and the risk of damaging susceptible metals. Vinegar and citric acid are two traditional choices for cleaning potable water systems, both in RVs, boats, hospitals, and in poultry watering systems. After as 3-6 hour soak, a 1-3% acid concentration will kill more than 85% of giardia cysts, and after 24 hours they will kill over 98%, something bleach cannot claim. The acidity dissolves their protective coat and the scale and biomass layers they are hiding under.

Don’t mix any acid with bleach, in the mistaken belief this will be a one-step miracle. The acid will cause the rapid release dangerous amounts of chlorine gas. If you chose to follow acid cleaning with bleach sanitation (probably not needed) be certain to rinse the plumbing with copious tap water to a neutral pH before adding bleach.

White vinegar is certainly the more available, but we’re recommending you give citric acid a try. It is a more effective descaling agent, in part because it is a double acid, and it has many uses around the boat (see “Passivating Stainless on Sails and Gear,” PS March 2022). It removes scale with less damage to underlying metals, you avoid the stink, and it is cheaper.

We’re not saying you need to acid wash your plumbing. If it has been well maintained, probably not. But a new-to-you boat that has been neglected, or if bleach sanitizing has not resulted in fresh water, an overnight soaking in vinegar or 3-5% citric acid could do the trick.

Drew Frye
Drew Frye, Practical Sailor’s technical editor, has used his background in chemistry and engineering to help guide Practical Sailor toward some of the most important topics covered during the past 10 years. His in-depth reporting on everything from anchors to safety tethers to fuel additives have netted multiple awards from Boating Writers International. With more than three decades of experience as a refinery engineer and a sailor, he has a knack for discovering money-saving “home-brew” products or “hacks” that make boating affordable for almost anyone. He has conducted dozens of tests for Practical Sailor and published over 200 articles on sailing equipment. His rigorous testing has prompted the improvement and introduction of several marine products that might not exist without his input. His book “Rigging Modern Anchors” has won wide praise for introducing the use of modern materials and novel techniques to solve an array of anchoring challenges. 


  1. Hi Drew,

    We have a 1994 90 gallon poly water tank with an unknown history, and in the 2 years we’ve owned it the water has always been cloudy, pretty disgusting looking, and we certainly don’t drink it. I’d like to try citric acid cleaning/descaling as you suggest. Is the 3-5% solution based on weight? For example, 90 gallons = 675 lb of water, multiplied by .03-.05 = 20-34 lb of citric acid powder? Yipes, that’s a lot of powder! Is this the correct way to calculate the ratio?

    Thanks much,

    Ron Wilander

  2. For large tanks, there is no reason to fill the tank with the required acid solution. That would require a lot of acid. Instead, mix the solution in a pump-up sprayer and use that to wet the sides of the tank. Repeat several times, at about 15 minute intervals. After soaking for a few hours, pump a few gallons through the plumbing at let that soak. Finally, wash it down with a freshwater hose, refill with water, and drain again.