How to sanitize your yacht's water tanks.

How to sanitize your yacht's water tanks

If you had to fill up your tanks with water from a stream or lake, or if the tanks have been contaminated in some other way, you will need to do a more thorough cleaning and sanitizing when you reach a (hopefully) clean municipal water supply.

1. Completely empty the water tanks.

2. You can sanitize the tanks by adding 300ml (one cup) fresh (not stored) unscented household bleach for each 190 litres (50 gallons) of water you add to the tanks.

3. A much better choice is to sanitize them with the EPA recommended concentration of chlorine dioxide. 

Advantages of chlorine dioxide over laundry bleach

• Biofilm control: Chlorine dioxide penetrates and breaks down the slimy film lining tank walls and hoses. Bleach mostly attacks the surface layer, so growth can return quickly. Biofilm is the usual cause of recurring odor in yacht tanks.
• Works across pH: Bleach loses much of its killing power as pH climbs above about 7.5 to 8. Chlorine dioxide stays effective across a much wider range.
• Fewer harmful byproducts: Bleach reacts with organic matter and forms trihalomethanes and other chlorinated compounds. Chlorine dioxide produces very little of these.
• Better taste and smell: Crews often notice a cleaner taste, without the swimming-pool odor bleach leaves behind.
• Gentler on hardware: Bleach adds chloride, a known cause of pitting and crevice corrosion in stainless steel tanks and fittings. It can also degrade rubber seals and gaskets over time.
• Stronger against resistant pathogens: Chlorine dioxide handles Giardia, Cryptosporidium, and viruses better than free chlorine at comparable contact times.

To disinfect your water system add 35 ml of a 3000 ppm Chlorine Dioxide solution or 5 ml of 20,000ppm Chlorine Dioxide solution for every 100 litres of tank water. 

There are 3 options for getting a Chlorine Dioxide solution.

1. Buy Ready made 3000 ppm Chlorine Dioxide solution on Amazon. A 4 ounce (120ml) bottle costs about US$12 and will treat 340 litres of water for about 3.5 cents/litre.
2. Buy a kit to make the chlorine dioxide gas on Amazon The kit has one bottle of hydrochloric acid and one bottle of Sodium Chlorite solution. When mixed together it makes 240 ml of 20,000 ppm ClO2. Enough for 4,800 litres of water at 0.7 cents per litre. 
3. Make your own kit for generating chlorine dioxide. 

We use option 3 and make our own chlorine dioxide. 

It’s more complicated, but much less expensive will last you for years and we use it for much more than sanitising the water tanks. It's perfect to sanitize vegetables, treat cuts and wounds, insect bites, etc. 

The primary advantage of making your own chlorine dioxide for active long time cruisers is ordering once and having it aboard for years of cruising.

Buy 1 Kg 80% Sodium Chlorite Powder on Amazon. and purchase a bottle of hydrochloric acid locally from any large hardware or supermarket.

To use the powder you need to dissolve it in distilled water. Here’s how to do it.

To make 500ml of a 22.4% Sodium Chlorite solution 

1. Slowly add 140 gms of 80% NaCl2 Flake into a glass container with 500ml of warm water, stirring with a plastic spoon until the Sodium Chlorite is dissolved. It should be a clear yellow solution when done.
2. Close the glass container with a glass or plastic lid, put it in a dark place. It does not ever go bad and you can use it for years.
3. After 24hrs slowly pour the solution through a coffee filter into a 500 ml dark glass bottle with a glass or plastic top. Keep the bottle in a dark place until needed.

To make 500ml of a 4% HCL Activator Acid

(Note: Use plastic gloves when working with Hydrochloric Acid and take care to not inhale the fumes. If you accidentally spill it on your skin, immediately wash with plenty of plain water.)

Buy a litre of hydrochloric acid (HCL) with no additives and 4 litres of distilled water from a large grocery store or hardware store. The acid, HCL comes in different strengths and you will need to dilute it to a 4% solution.

To create a 4% solution of HCl divide the strength of the solution you bought by 4 to determine how much distilled water you need to dilute your HCl.

For 23% HCl, divide by 4% and you have 5.75 parts. So, to make 500 ml of 4% HCL you would use 87 ml of 23% HCL and 413 ml of distilled water.

For 35% HCL divide by 4% and you have 8.75 parts. To make 500 ml of 4%HCL you would use 57 ml 35%HCL + 443 ml distilled water.

To Sanitize Your Water Tanks

Mix one part sodium chlorite solution with one part 4% HCl (hydrochloric acid), wait 30 seconds and pour the activated solution into your water tanks. Take care not to inhale the fumes from the activated solution. 

You will need 5ml for every 100 litres of water in your tank. If you have more than one tank and they are full, add the correct amount into each tank. 

If you are filling your tank with shore water add the mixed solution to your filler hose and then fill the tanks.

.Remove any interior water filters, open the water valves, and run the fresh water pump to allow the sterilized solution to treat the entire system, then wait 8 to 12 hours, drain all the water out of your tanks, and refill with good, pre-filtered water.

Or, better yet, refill the tanks with desalinated water!

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