Re: SPACE: How hard IS it to get off Earth?
Mon, 22 Nov 1999 03:33:54 -0500

On Sun, 21 Nov 1999 11:25:06 -0600 "Billy Brown" <> writes:

> On the same vessels the entire fresh water supply is extracted from
> sea
> water by mechanical systems. While this is a somewhat easier
> problem than
> extracting water from sewage, it illustrates that it is pretty easy
> to get a
> steady stream of potable water from a large uniform contaminated
> source. It
> should also be noted that this was accomplished in the '60s without
> a
> particularly large R&D investment - on can reasonably assume that a
> similar
> effort today could achieve similar results from a wider variety of
> inputs.

It is well known that pure water can be obtained from contaminated water by a process of evaporation and condensation, which is sometimes called distillation. When that is done as an intentional activity, the cost of the resulting purified water is exorbitantly high relative to what people are used to paying for tap water or agricultural/industrial water, since the process is energy intensive. On a nuclear powered ship (submarine or surface) there is plenty of energy available, so that technique could be used. But still, it would probably be cheaper for a nuclear powered surface ship to store fresh water obtained from on-shore sources than it would be to make fresh water from seawater.

Almost all of the tap water and agricultural/industrial water consumed in the world comes indirectly from the sea, and most of the purification is accomplished by a process of evaporation and condensation. The trick is that the evaporation and condensation step in the purification process is accomplished free of cost since it happens naturally without any effort on the part of man. Seawater evaporates and comes down as rain, and the rainwater is collected in rivers, lakes, and groundwater. Nearly pure water can be collected from those sources, and the additional processing to make the water safe to drink can be done cheaply. Those processes are settlement, filtration, and disinfecting (usually with chlorine). Distribution is done under pressure to prevent the introduction of contaminants during distribution.

Ron Kean



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