How to sanitise your yacht's water tanks.

 

 Sanitizing Contaminated 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 sanitising 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 sanitise them with 10ml of 22% chlorine dioxide for each 100 litres of water.

To disinfect your water system at the EPA recommended 1ppm 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.

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.

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 236 ml of 20,000 ppm ClO2. Enough for 4,700 litres of water at 0.7 cents per litre. This kit has 120ml of Sodium Chlorite solution and will make 3,571 ml of Sodium Chlorite Solution, enough to sanitise 140,000 litres of water.

Make your own kit for generating chlorine dioxide. This is what we do. It’s more complicated, but much less expensive will last you for years and we use it for much more than sanitising the wter tanks. It's perfect to treat cuts and wounds, insect bites, sanitise vegetables, etc. The primary advantage of making your own chlorine dioxide for active cruisers is ordering once and having it aboard for years of cruising.

Buy 1 Kg 80% Sodium Chlorite Powder on Amazon. and purchase 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 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.

Close the glass container with a glass or plastic lid, put it in a dark place. After 24hrs there may be some sediment on the bottom and possibly an oily film on top. Skim off the oil with a plastic spoon and slowly pour the solution into a 500 ml dark glass bottle with a glass or plastic top. Don't pour in the sediment at the bottom of the mixing container. Keep the bottle in a dark place until needed.

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.

Sanitizing 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. 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 add the mixed solution to your filler hose and then fill the tanks.

Take care not to inhale the fumes from the activated solution.

4.  Remove any interior water filters, open the water valves, and run the fresh water pump to allow the sterilised 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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