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Harvesting Rainwater on your Boat

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Water is vital to life and a precious commodity these days. In the Caribbean – despite the vast amounts of rainfall we seem to experience – water supplies can often dwindle or even become contaminated after the passing of a hurricane, so it pays to have your own backup supply.  Time to learn how to harvest rainwater.

Take a hike inland and you’ll see almost every dwelling has a huge water butt that fills through a pipe from the gutters. Despite being short in minerals and salts from mountain and river, rainwater, in its purest form, is the sweetest of them all.

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Humans need approximately half a liter of water per day to survive and two liters to avoid thirst.

Even today, when watermakers are the norm on many cruising boats, there are a lot of ingenious ways of harvesting rainwater to supplement your supply. These include especially designed rain catchers, converted Biminis, sun covers, and awnings modified with through-hull fittings, gutters and hose pipes all adapted to catch water and channel it into tanks or jerry jugs.

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How do you catch rainwater on your boat? Photo by Rosie Burr
How do you catch rainwater on your boat?
Photo by Rosie Burr

Some boats build dams around their on deck filling ports and scupper drains which divert rainwater to the tanks through Y-valves. I have even seen pieces of yarn pegged to Biminis and directed into a bucket. Whatever method you choose, it can be tailored to suit your boat.

Whether it is for convenience or cost, environmental reasons or the simple pleasure of getting it for free, harvesting rainwater should be carefully considered especially in terms of drinking water.

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Air pollution from industry or highly populated areas can be a cause for concern while harvesting rainwater though this is less likely for most of us sailing in the Caribbean.

Saharan dust blown across from Africa, may cause more of a problem although there seems to be little information on the effect this has on drinking water, you’ll want to avoid consuming it. The water catchment area is also where biological or chemical pollution can occur. Decks and rain catchers in the form of Biminis or other permanently-mounted outside fittings need to be free from salt, debris and other contaminants such as spilt diesel or oil, dirt from shore-side visits and bird poop. A first flush diverter or a way of letting these areas wash off is a necessary first step when harvesting rainwater.

Once you have decided on your method of harvesting and storage, the next job is to put the first filter in place.

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This can be as simple as a piece of mesh or gauze (or even coffee filters – not paper ones) secured over the scupper drain or tank filler. This is to stop any large particles like dead insects or grit from entering the tanks.

Ideally, the water should then be held in an isolated tank in case it becomes polluted. The tank should be solid, sealed and safe from leaks and contaminants.

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With so much rain in the Caribbean there is no reason not to harvest any. Photo by Rosie Burr
With so much rain in the Caribbean there is no reason not to harvest any. Photo by Rosie Burr

It is a good idea to have two water filters in place when harvesting rainwater

Some recommend having two filters in tandem – a course one and a fine one. Others suggest placing a course filter before the pump to stop it from blocking and to protect it from damage, and another finer charcoal or ceramic filter before the tap/faucet to remove pathogens and finer particles. These are readily found on the market today. It is important to keep an eye on the filters and change when necessary. They can be a breeding ground for bacteria if not maintained.

If in any doubt about the purity of the water it can be disinfected either by boiling for five minutes

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This is best if you don’t want to add chemicals, or by treating with small quantities of chlorine, the cheapest method. Ideally five to eight drops of general unscented liquid household bleach containing 5.25 – 8.25 percent chlorine will treat one gallon of water, a little more if it is cloudy. That’s approx ½ – 1 teaspoon per five gallons. It is best to let it stand for a couple of hours first before drinking. Chlorine will kill most common bacteria. Finally, periodically clean out your tanks thoroughly by scrubbing and washing out with chlorine.

Harvesting rainwater for drinking purposes is a controversial subject. It is a matter of personal choice, taking into consideration the area you cruise, local air pollution, your lifestyle and your particular water catchment system.

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Treating water with household bleach containing 5.25-8.25 percent chlorine

Volume of Water to be Treated:                             Bleach Solution to Add:

1 quart/1 liter                                                                         5 drops

1/2 gallon/2 quarts/2 liters                                                10 drops

1 gallon                                                                                    1/4 teaspoon

5 gallons                                                                                  1 teaspoon

10 gallons                                                                                2 teaspoons

Caution: Bleach will not kill some disease-causing organisms commonly found in surface water. Bleach will not remove chemical pollutants

Source: Washington State Department of Health

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Rosie Burr
Rosie Burr
Rosie and her husband Sim Hoggarth on yacht Wandering Star have cruised the Caribbean and North America fulltime for nine years.

So Caribbean you can almost taste the rum...

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