Keeping Water Clean and Fresh

Good old bleach is great, but treatment tabs have advantages.


In the first part of our three-part series covering onboard water quality, we discussed protecting the tank with basic filtration and securing the tank vent. Further action is required, however, as the tank and its contents will always be far from sterile.

Municipal water is filtered to remove turbidity, disinfected (typically with chlorine, ozone, or ultraviolet light), filtered once more (often very fine filtration to remove cryptosporidium cysts, which resist disinfection), and disinfected once more (with chlorine or chloramine) to protect the water while its in the distribution system. However, since we are storing the water on our boats, this process of secondary disinfection becomes our responsibility. So what are the options for treating water that is already in an onboard tank?

Star brite Water Treatment

In the U.S., the chlorine residual from municipal waters secondary disinfection is usually enough to keep tank water clean. In most cases, a sufficient amount of chlorine-1 part per million (ppm)-from the municipal treatment process carries into the boats tank. You can easily check the amount of chlorine in your tank by using the test strips designed for aquariums. We like the Tetra EasyStrips (about 69 cents per test), which simultaneously test for nitrate, nitrite, hardness, chlorine, alkalinity, and pH.

Over-chlorinating, whether with bleach or commercial freshening chemicals, can shorten the life of elastomers in your plumbing. Chlorine is a leading cause of death for freshwater pump impellers. Excess chlorine also shortens the life of tap-water polishing filters (which we will discuss in the next installment of this series). Finally, excess chlorine has negative health effects and is limited to 4 ppm by U.S. drinking water standards (0.5-1 ppm is normal). If you find that your tank lacks any residual chlorine, there are a few treatment options:

Bleach: Household bleach (unscented) typically contains 5.25 percent sodium hypochlorite, which breaks down in water into hypochlorous acid and several other useful sterilizing agents. Only a few parts per million are needed to effectively deactivate bacteria and viruses, typically within two to 30 minutes, depending on temperature and contaminant levels. However, there are a few caveats. The water must be reasonably free of physical dirt, since the bleach will expend itself oxidizing organic materials, and bacteria will hide within the dirt.

How much bleach should you use? More is not always better. The standard recommendation for emergency disinfection is 1 tablespoon per 10 gallons; this standard is frequently repeated in boating and camping texts. This allows for organic compounds chlorine demand and provides enough kick-20 ppm of free chlorine-to reach micro-organisms buried inside small dirt particles. This is appropriate for sanitizing and for dirty water, but it is overkill for routine treatment of good quality water, at least 10 times more than is typically used in tap water.

For treating water that is clear and chlorinated at the tap, 1 teaspoon of bleach per 50 gallons will provide a 2 ppm booster, the very most that should be needed. Chlorine aftertaste is the most common onboard water-quality complaint; however, chlorine at the tank can be efficiently removed with carbon filtration (covered in part three of this series). In fact, chlorination is vital to performance of downstream filtration, controlling growth within the filter.

Dichlorisocyanurinate: Common in swimming pool tablets, chlorine in this form has several advantages. Chlorine levels are stabilized by a chemical equilibrium, resulting in a more stable and more durable treatment, and reducing the amount required. Additionally, the released chlorine generates cyanuric acid, an effective corrosion inhibitor for aluminum, reducing aluminum corrosion by 10 to 40 times compared to bleach treatment. Both the U.S. Environmental Protection Agency (EPA) and World Health Organization (WHO) approve this method.

Hydrogen peroxide: Internet forums frequently suggest the use of hydrogen peroxide (H2O2) as a bleach alternative, but because of the lack of regulatory guidance (neither the EPA nor WHO recommend it as a treatment solely on its own) and numerous well-known shortcomings, we cannot recommend it as a sterilizing agent.

Quaternary amines: Common in non-bleach, anti-bacterial surface cleaners and hand soaps, quaternary amines (e.g. benzalkonium chloride) are effective against bacteria, algae, and most viruses. However, they are typically very toxic to marine invertebrates (a few ppb is lethal), so use around the water should be limited. If you are sterilizing a tank with these, they should be flushed from the system before drinking.

Ultraviolet light (UV): Ultraviolet light, specifically those wavelengths between 250 and 300 nanometers, is a very effective sterilizing agent. UV is typically employed as a final sterilizing step, in the plumbing, and not in the tank. Weve tested two portable UV devices for personal water purification, the Steripen (see PS, April 2008 online) and the CamelBak All Clear (see Chandlery, PS, June 2013 online).

Desert island tip: Lets say youre down to your last bottle of water, and although you have fresh water available, you have no chemicals or filters to make it safe to drink. What to do? WHO has studied this problem, as it is not unusual in the wake of a hurricane or flood.

First, collect the best water you can find in clear water bottles, allow the water to settle, and filter it through cloth until it is reasonably clear. Fill the bottles about three-quarters full, shaking vigorously to oxygenate the water, and then, leave the water in full sun (placing the bottles on a reflective surface helps) for three to eight hours. The suns UV will deactivate over 99.9 percent of the pathogens in the bottle.

None of the above methods will remove microscopic parasites (giardia and cryptosporidium). These are shell-like organisms that resist chlorine treatment; water suspected of containing parasitic cysts must be filtered to 0.5 microns to provide physical removal. We will deal with physical filtering at the tap in the final segment of this series.

What We Tested

There are commercial products designed to accomplish the same water-purifying tasks as bleach, but they claim they do it better. For this report, we tested tank-cleaning products, sanitizing chemicals, and tank-freshening chemicals, as well as a dishwasher detergent.

Intended to cleanse funky tanks before sanitizing, tank-cleaning products contain non-bleach cleaners and sanitizing agents. While they should not be needed in a well-maintained system, they may be helpful if things have been let go.

Sanitizing chemicals are for used after cleaning; all are based on chlorine, but the chemistry varies. Tank-freshening chemicals provide disinfection for clean tanks, supplementing the chlorine in the tap water. These are handy when you don’t trust the tap water-perhaps the water has been sitting for a while and seems less than fresh.

How We Tested

We dosed each freshening product into reverse osmosis (RO) water as directed by the manufacturer, measuring free chlorine and observing odor. We then transferred the water into 1-gallon, disposable ice-tea jugs made of thick-walled polyethylene, which we felt presented a reasonable surrogate for a lightly contaminated polyethylene water tank. Although well-rinsed when emptied, they had a uniform level of taste and smell saturated into the plastic; we graded how well the chlorine residual endured after 24 hours, and how well residual odor and taste were removed.

We then repeated similar tests for tank cleaning-chemicals and tank-sanitizing chemicals. We also placed aluminum corrosion coupons (SAE 329) in the solutions and graded them after regular checks during a three-week period; chlorine-induced corrosion is a major concern for those with aluminum tanks. Note that all testing was with high-quality RO water; other water types may exhibit some chlorine demand (some bleach is neutralized by the water), and some will contain chlorine. The only way to be certain of dosage is to test with swimming pool strips or equivalent.

We tested tank-cleaning products by soaking contaminated beverage containers and soaking dishes uniformly soiled with dried-on salsa. Water and a bleach solution recommended for sanitizing by the American National Standards Institute (ANSI) were controls.

We also used each of the freshening chemicals during a summer of cruising, dosed as recommended. Because the filling water was variable, we did not attempt any quantitative measurement in the actual onboard field trials. We simply evaluated taste.


Here is a rundown of some important observations that testers made during the evaluation.

Any additives should be used during the first one-third of the filling process. This allows a thorough mixing. All of the tablets dissolved before the tank was full. For aluminum tanks, dissolve the tablets in a bottle of water first.

Bleach is a handling problem. We settled on a sturdy pint sports drink bottle with a cap that held the required amount. We kept the bottle in a deck locker to avoid dribbling the bleach on clothing, upholstery, or carpet. For annual sanitizing we filled a water bottle with the required dose at home and took only that to the marina. Camco TastePure Freshener contains diluted bleach and is less of a bleaching hazard if spilled. All other products were non-bleaching; nevertheless we would still clean up all spills and keep them away from fabric.

While some of the products left a detectable chlorine smell in the tank, none were noticeable at the tap, even without carbon filtration.

We were concerned about pitting in aluminum tanks. The highest concentrations were in the tank cleaning and sanitation products. Since these are only used once a year for no more than 90 minutes while the tank is being cleaned and flushed, we limited the test coupon exposure to only 48 hours. None of the products caused significan’t pitting, but Puriclean (dichlorisocyanurinate) was clearly less corrosive to aluminum than other sanitizing treatments. When we tested freshening treatments and tap water, we found the same trend; AquaMega Tabs (also based on dichlorisocyanurinate) were far less damaging than other treatments, and less damaging than tap water alone.

While most disinfecting products are based around 2 to 3 ppm of free chlorine, 0.5 ppm residual chlorine is enough for safe water, and owners of aluminum tanks should buy test tapes and use only the minimum amount of disinfectant required.

We tested some non-chlorine treatments (ozone and hydrogen peroxide), but found these to be either corrosive to aluminum or ineffective. Carefully regulated chlorination is the most sensible treatment.

Tank cleaning chemicals function a little differently than bleach and detergent, dissolving more material without agitation, but not loosening heavier deposits as well as detergent with light agitation. They did perform better than plain water or the ANSI bleach sanitizing solution. All were non-corrosive to aluminum. The sanitizing effect of the quaternary amines and peroxides may be valuable, if the user does not intend to follow cleaning with a bleach sanitizing process.

aluminum coupons

Tank Cleaning Chemicals

Star brite Tank Cleaner

Star brites Water Tank and System Flush, also labeled as Aqua Clean Water Tank Flush, is based on alcohol and alkylbenzly chloride, a quaternary amine commonly used in anti-bacterial handsoaps and surface cleaners. It is more potent than plain bleach sanitizing solutions. However, we cannot confirm the effectiveness of this chemistry.

We do not advise adding bleach to the product, as an undesirable reaction will occur. Any bleach sanitizing, if desired, must be a separate step.

Bottom line: Recommended with a bleach follow up if fail-safe sanitizing is required.

Camco Spring Fresh

Camcos Spring Fresh contains a food-grade surfactant and is a better cleaner than plain bleach sanitizing. As with the Star brite, we caution against adding bleach to the product as a bad reaction will occur. If you plan to do bleach sanitizing, do it in a separate step.

Bottom line: Recommended if fail-safe sanitizing is required. Follow up with bleach or Camco Dewinterizer.

Finish PowerBall Tabs

Our research into the chemistry behind tank-sterilizing tabs led us to regular dishwashing tablets. Finish Powerball Tabs were the ones we had on hand, so we included them in the test. They required slightly more agitation than the other test products, but they did a superior job when gentle swirling was added. Like all dishwasher detergents, Powerball Tabs contain a sterilizing agent (in this case, percarbonate, which releases hydrogen peroxide) to prevent the dishwasher from getting nasty. We used 1 tablet per 5 gallons of water, which we felt mimicked the solution used in a dishwasher.

Bottom line: This is the Budget Buy choice, if you have the time to take your boat for a rollicking sail to provide some agitation.

Tank Sanitizing Chemicals

These treatments are meant to be done once a season (often after winter storage) or when you suspect a contaminated tank.

Puriclean Clean Tabs

These tabs are based upon sodium dichlorisocyanurinate, and have the same basic chemistry as AquaMega Tabs (below), but are packaged in a tub suitable for tanks up to 60 gallons. To uses, you dissolve the tabs in about gallon of water, then mix it into the tank and allow it to sit for 1 to 2 hours. This concentration (about 20-30 ppm chlorine) sanitizes any pre-cleaned tank. Testers noted much lower aluminum corrosion rates than other sanitizing products; the aluminum is discolored by the formation of a dark passive layer, which stops further corrosion and pitting.

Bottom line: Recommended. The stable residual and low aluminum corrosion rates make Puriclean Clean Tabs the PS Best Choice among tank sanitizing chemicals.

Star brite Water Shock

A concentrated formula, Star brites Water Shock is intended to clear up any odors and tastes that tank cleaning leaves behind, and to sanitize the tank. It is also recommended for routine freshening at a lower dosage.

Bottom line: We don’t believe this outperforms the ANSI bleach sanitizing procedure (below).

Camco Dewinterizer

Camcos Dewinterizer uses a somewhat lower chlorine content than recommended by ANSI. It is intended to clear-up odors and tastes that tank cleaning left behind, and to sanitize the tank.

Bottom line: We don’t believe this outperforms the ANSI bleach sanitizing procedure.

Tank Freshening, Disinfection Chemicals

These treatments are meant to be done on a routine basis, either to restore freshness to stale water or to maintain clean tanks.

Household Bleach

Unscented, 5.25-percent sodium hypochlorite (household bleach) is sold under countless brands. The baseline for comparison, WHO and the EPA has studied this ad nauseam. A solution of 1 teaspoon per 50 gallons gave us a 2 ppm residual; about right for most tap-water applications. Remember that bleach loses effectiveness after long storage and should not be kept more than six months after opening.

Bottom line: This is far and away the most affordable treatment, but you must measure it yourself-and don’t spill.

tank cleaners

AquaMega Clean Tabs

Based on sodium dichlorisocyanurinate, the AquaMega tablets are available in amounts matched to tank sizes. We observed a more stable residual and much lower aluminum corrosion rates. There was a stable residual for weeks, versus only 48 hours with bleach products. Because of this stable residual, we suspect that the AquaMega tabs dose might be stronger than what most tanks will require for simple freshening.

If you are willing to test your water, you can tailor a smaller dose that more closely mimics the ANSI solution. If the 50-gallon size is more than you need, you can break tabs in half and wrap-up the remainder in the foil pouch for up to one month. Its also available in small pills (Aqua Minitabs) for individual treatments.

Bottom line: The convenient packaging, low corrosion rates, and stable residual made this our Best Choice among tank freshening and disinfection chemicals. It was also our favorite to use.

Star brite Freshener

The Star brite Water Freshener was the only solution in the test lacking the distinctive chlorine odor, but it did not change the odor of our chlorinated tap water. The manufacturer did not share the disinfectant chemistry, so we could not confirm its effectiveness.

Bottom line: While the lack of chlorine smell in the concentrate suggested better tasting water, we observed no difference on the boat.

TastePure Freshener

Based on pre-diluted bleach, TastePure Water Freshener performed much like bleach. The resulting water had a barely discernible chlorine smell, and the taste was fresh.

Bottom line: Recommended as an effective freshening product.


The United States has perhaps the highest quality water in world, regardless of what we read in the papers. Do we need to disinfect if the source water is chlorinated and of high quality? Perhaps not for safety alone, if the tank is cleaned and the water is turned over every few weeks, though often potability is improved. If traveling outside the U.S. or if cautious by nature, providing secondary disinfection is easy and safe.

We like bleach, particularly for annual sanitizing. Its cheap, its known to be effective, and any aftertaste is easily removed with carbon filtering. However, the two test products formulated with dichlorisocyanurinate-AquaMega Tabs for freshening and Puriclean Powder for sanitizing-lasted longer than bleach. We also like AquaMega tablets for convenience; they have a long shelf life and are simple in use, with nothing to measure, nothing to spill, and nothing to return to stowage after use. If your boats not in the water and you can’t agitate your tank, the cleaning chemicals seem to help loosen deposits better than bleach sanitizing solutions and dishwasher detergents. However, dishwasher detergent did very well when a little sloshing was provided.

Although we began this project expecting cheap and effective bleach would win out, the convenience of some of the commercial products won us over.

For sailors with aluminum tanks, we recommend AquaMega Tabs and Puriclean because of much lower corrosion rates-even lower than tap water. Additionally, we believe that the manufacturers recommended dose may be quite conservative; half this amount may be sufficient. We recommend that you buy test strips and use the smallest dose that is detectable or produces any chlorine smell in the tank. Aluminum corrosion will be reduced.

In our final clean-water installment, we will explore point-of-use filters, which will remove any last trace of odor, taste, or contaminating chemicals, leaving water as fresh, pure, and safe as bottled water. However, the steps we explored in this and the previous report (see PS, June 2015 online) are just as critical. Protection against biological growth begins at the tank fill and the tank.

Water Treatments & Tank Sanitizing
Tank Cleaning
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. Excellent article(s), all 3 of them. I learned a lot. Biggest frustration is sourcing the Best Choice Aqua Mega Tabs. They are not available in the US. I can’t imagine why more marine supply stores don’t offer them.


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