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The squalls continue to roll through Grenada, and as the rain falls from the sky, we continue to catch it. Up to this point, we have only been using this fresh water to wash dishes. I do know that a lot of people add rain water that they collect to their main water tanks, using it for cooking, drinking, etc. The thought of doing that has always made me a bit nervous.

Sail Delmarva wrote a good post about how to filter rainwater before adding it to your tank. Boat Bits has a good post on filtering the water at the other end.

Do you add rain water to your tanks? If so, do you filter it? How?

We found all this fresh water yesterday.


  1. I wrote a 4-part series on water treatment for Practical Sailor. The bare nuts are:

    1. Filter the water going in. This is to catch gross junk and because step 2 won’t work if there is dirt in the tank. The bag filter idea I worked up for some friends in MD keeping a PDQ on a mooring. Simple, cheap, and easy to maintain anywhere.
    2. Sanitze the tank with bleach. No, hydrogen peroxide does not actually work in any practical dose (if you use enough you are over the healthy exposure limit), and there are no protecoles for its use on drinking water.
    3. Secure the tank. Look for the vent and make sure there is a bug screen. This is code, but most builder miss it.
    4. Filter. An NSF 53 rated carbon block filter will do 2 things; remove any excess bleach (the carbon reacts with a bleach making a few ppm of CO2 and salt) and any cysts (cysts can resits bleach bacteria and viruses cannot.

    Another interesting thing to do, if you are interested in rainwater, is to Google rainwater safety in areas where it is a common drinking water source. Australia is a good source of information, and the US desert areas. Since human waste is basically impossible, it turns out that it is quite safe. Marine rainwater should be even safer.

  2. My favorite source of filters is The 2×10 Pentex G4 slimline is universal globally; filters are available most anywhere. Better than a proprietary system, IMHO. Doulton Sterisyl is also very good, available for 2×10 housings.

  3. We’ve been catching and drinking rainwater for 6.5 years with no ill effects. We have two water tanks, forward for shore and rainwater, aft JUST for water maker water. We filter rainwater at source just using a fine mesh fabric. We use a small piece of what looks like “curtain shear material” to act as a gross filter. At the galley tap, ALL our drinking water passes through a Sea Gull filter, regardless of which tank it comes from – the filter is changed annually. We do not add bleach or any other chemicals to our tanks, because they are aluminum. When we add shore water to our forward tank, we filter out chlorine with a filter from Home Depot, carbon I think. Our water pump is also protected with a small mesh screen, which is cleaned annually. When at dock for a week or more, we connect directly to our water supply, bypassing the tanks and pump – through a pressure step down.

  4. Sailors aren’t the only ones with water treatment issues. There are proven, extremely reliable, cost-effective treatment systems available for rural / off-grid houses and cottages that work very well aboard ship for a fraction of the cost of “marine” gear.

    My preferred system:

    1. Filter the water going into the tank, to remove visible debris. The bag filter Drew mentioned earlier should be great for this.

    2. Keep a moderate chlorine level in the fresh water tanks. (Tanks plural – it’s much better to have several small tanks than one big one.)

    3. Assume the water in the tanks is biologically unsafe anyway. Thus, the line from the tank to the potable water taps is:
    – Pump
    – Sediment filter
    – Carbon filter
    – UV sterilizer (I have a Sterilight S8Q-PA on my home system, and would likely want its smaller 12V cousin, the S2Q-P-12VDC, on a boat). It only uses about 17 watts, and kills *everything*.

    Don’t go “marine grade” for any of this. The sediment and carbon filters are standard 40-litre-per-minute filters from GE, Pentek, etc. off McMaster-Carr for $25, and each filter cartridge (lasts about a year) is eight bucks. The Sterilight is the pricey part, at $400-odd for the hardware and $40 a year for replacement bulbs, but it virtually guarantees you’ll never get any nasty biologicals in the drinking water.

    Anyway, that’s my $0.02 worth. And it comes endorsed by a *lot* of water system experts and health officials I’ve talked to about this.

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