Freshwater to seawater ratio - SailNet Community
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post #1 of 31 Old 04-16-2007 Thread Starter
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Freshwater to seawater ratio

Here's a question that occured to me while planning my escape. Let's say you are offshore and the watermaker goes south or water is short for any other unplanned event. How much seawater can be added to fresh to extend it without causing serious harm?
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post #2 of 31 Old 04-16-2007
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I'd say it depends on your health, the state of your kidneys and liver, the salinity of the water, the temperature, and a few other things...

Someone with compromised kidneys may not be able to drink as high a percentage of salt water as someone who is perfectly healthy. Some one with high blood pressure probably would have problems with vastly increasing their salt intake as well.

The saltier the water, the less you would be able to add by volume. In hot weather, your tolerance for salt water probably goes up, since you tend to lose salt via perspiration.

I'd imagine that the duration of the ordeal would make a difference as well. The shorter the period of time, the higher the salt water percentage could be.

My advice is try like hell not to get into such a situation. Carry spare parts and if your watermaker is only power driven.... you might consider investing in a small hand-operated one. Relying on a watermaker, on a small boat, where the electrical and other systems aren't redundant and very vulnerable to failure is a bad survival tactic. You should generally carry enough water to get you to the next port in the case of a watermaker failure. If you're convoying with other boats, this may not be as necessary, but if your on your own... I'd consider it prudent.

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post #3 of 31 Old 04-16-2007
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It's why I'm going to incorporate a rain-catching design into my bimini. I don't want a watermaker for the boat, but I want a hand-operated one for the liferaft...absolutely!
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Catching rainwater is a great idea, and many have used it...but you need to make sure you have the proper equipment to filter and treat it so that it is potable.

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post #5 of 31 Old 04-16-2007
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How many ppms of salt or total dissolved solids (TDS) are you getting from your RO system? Do you have a TDS meter? Use this simple formula to perform calculate the volume needed to reach the desired concentration.

V1xC1 + V2xC2 = V3xC3 V = Volume C= Concentration,
V1 + V2 + V3
or V2 = ((C3-C1)x V1)/ (C2-C3)


If you have 50 gallons of water from your water maker @ 600 PPMs TDS, V1 and C1.

Your will be using salt water usually 35000 ppms, C2
C3 (lets say 1500) is the desired concentration PPMs of TDS of your total V3 volume

Yan can add 1.34 gallons of sea water to your tanks get 1500 vs 600. not wother the effort in my book.

According to World Health Organization (WHO): "The palatability of water with a TDS level of less than 600 mg/litre is generally considered to be good; drinking-water becomes significantly and increasingly unpalatable at TDS levels greater than about 1000 mg/litre."

PPMs = mg/liter


I looks like if it has too much salt it will no be palateble and you would not be able to dink it. On my previous job our standart was less than 1000 for long term (more than 1 week) and 1500 for short term (less than 1 week)
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post #6 of 31 Old 04-16-2007
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Bob's thirsty, now where did he put his calculator?

Why, in planning his escape, Bob intends to include a few jugs of fresh water, you know, just in case the r/o goes south. Float nicely behind the life raft they do, just remember to attach 'em with a length of line.

Supplement with sea water if you must, however, if you go nuts that's probably too much so adjust accordingly.

Rainwater and bird ****, essential vitamins and minerals ...

Christ Almighty, maybe you just better be safe and stay at home.

Valiente ... you one savy hombre!

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The Pardey's have written on methods of collecting rain water, rather extensively and ingeniously. You can filter it with a coffee filter if you like. The only treating you'll need to do is the chlorination of your tanks that you would normally do for offshore sailing.
Rain water is going to be more pure than any water you are likely to get anywhere in the world, even after it's run down your sails. Water purity becomes an issue when water is stored in tankage. Stored water allows bacteria to grow, a slight dose of chlorine nips it in the bud.

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post #8 of 31 Old 04-17-2007
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While rain water may be relatively pure, it will also have airborne contaminants in it... IMHO, it will need more filtering than a plain old coffee filter. It will have dust, mold spores, airborne chemicals, and other such things in it... If you want to drink them, be my guest... but I prefer not to.

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post #9 of 31 Old 04-17-2007
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Wanabe:

If you are close to shore you go to first pub and order water (or beer). Problem solved.

If you are far away from shore the air pollution is lower than in any urban area. You just have to let go the first shower to clean the air a little (it also washes the sails and the deck), then you are better off drinking rain then not to drink at all.
There are millions of people in the world drinking rain water. (Some get sick).
If you are on a boat you can boil that water to make it safe.
If you run out of gas you can make solar cooker from Alu foil and some other stuff you find on a boat (lots about solar cooking is available on the web, so get educated as part of good seamanship, you never know when you run out of gas.)
If you are in a raft your chances are limited. But better to drink rain water than sea water, Sea water will kill you in no time.
(if you had a survival hand operated water-maker you would not start this tread)
Coffee filter is a joke. Large particles of dirt are most likely not your worst enemy. Boiling water is the right way to go or proper filtering - some boaters equip their boats with good filters anyway to filter questionable water you get in marinas/gas stations. Chemical treatment is good too.
I have a portable carbon filter advertised to do the job - but I would prefer not to rely strictly on it - would boil as well.
Where I leave we have some rural areas where houses collect rainwater from the roofs and not long ago they used it for drinking. And most survived.
Now the only use it for watering the garden or wash the car and for washing machines (excellent as it contains no limestone). Even when I was a kid we drank it in some cottages in the mountains.
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post #10 of 31 Old 04-17-2007
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Quote:
Originally Posted by sailingdog
While rain water may be relatively pure, it will also have airborne contaminants in it... IMHO, it will need more filtering than a plain old coffee filter. It will have dust, mold spores, airborne chemicals, and other such things in it... If you want to drink them, be my guest... but I prefer not to.
Aye dog ... that rainwater is going to be full of the very contaminents you breath ... Bob agrees, you just can't be too careful ... TIC!

bob
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