[leebca]

There may be some concern or confusion about the water used in the marine aquarium.

Source water - This is the water used to make up marine water from artificial salts.

NSW - This is the acronym for natural sea water.

RO/DI - This is the acronym for reverse osmosis and deionized. Both are used together, usually DI first before the RO.

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There is no doubt that the best source water that can be used is distilled water. However, that is expensive on a large scale and, for other than an aquarium under 50 gallons, isn't too attractive.
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The next grade of source water is RO/DI water. It is desirable for most medium to small marine systems, but the RO portion of the treatment does waste water. It may take up to 4 times the water to get 1 part of RO water. Thus, up to 3 parts may be wasted in the sense that it goes down the sewer/drain.
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The next grade of source water is DI water. There are a couple of configurations of this treatment. The most common is sending the water through a single resin bed that takes out impurity ions and replaces them with 'safe' or acceptable ions. This is an exchange resin. A resin is specialized to the kinds of ions it will exchange. Another configuration is a double DI bed. One resin bed exchanges one kind of ions and that water then passes through a second resin bed where the other kinds of ions are exchanged. It's a double exchange with each resin exchanging different impurity ions. This water is about the best water quality that the process of de-ionization can produce. This water comes close to RO/DI water quality. This treatment wastes no water and is most likely pure enough for all marine aquariums.

The above RO/DI treatments of tap water still pose some exposure and risk that contaminants may get through the system that are undesirable for marine livestock. Two primary concerns: It is still worthwhile to verify the total dissolved solids (TDS) left in treated water and to test for ion ingredients, on a regular basis. The TDS of distilled water is 0.0 ppm. Keeping in mind the accuracy and reliability range, a TDS meter may have a range of results and still be reliable in a sense. These meters usually need calibration.

The TDS of RO/DI water should be below 10. ppm. Rarely does this water make it below 2 ppm, with the average being around 5-6. Besides monitoring this feature to verify the RO/DI treatment system is working properly, the aquarist may wish to test for small ions (iron, copper, etc.) in the water to verify these are not finding their way into the aquarium.

A third concern is organic materials. A good RO unit will prevent large dissolved organic molecules from slipping through, but can miss some organic gases. Still it doesn't hurt and is recommended to follow the RO/DI treatment with a chamber of activated carbon to polish any residual (organic gas, and ionic) components.
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The lowest grade of source water is tap water. Even if the aquarist tests that water for impurities commonly monitored in the marine aquarium (e.g., phosphate, nitrites, nitrates, ammonia, silica, iron, etc.) there is no way for all impurities to be tested. Anything can be in the tap water that is not harmful to humans but harmful to marine livestock. There are test kits to test for pesticides and other contaminants (e.g., the Watersafe All-In-One Drinking Water Test kit), but still these tests don't cover the entire range of impurities harmful to marine livestock. Another concern is the wide range of tap water quality from municipalities and different sources (e.g., well water, water table, lakes, etc.). The reader should refer to this reference for more information on tap water concerns: http://www.advancedaquarist.com/issues/jan2004/chem.htm
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Natural sea water would seem to be the best choice for water changes in the marine aquarium. However, where can it be gotten? Much of the USA coastal areas are polluted. NSW shares a common concern with tap water purity in that the aquarist can't test for everything that might be in the water. There is some minimal exposure to acquiring disease and undesirable organisms through the use of NSW.

I've tested (analytical chemical analysis) NSW that was sold as 'not polluted.' I have found petroleum and fuel products in some of them. A rather humorous event was a person who went 25 miles out to sea and collected water in vats. The vat water showed petroleum products that matched those used by the boat. The person literally brought their own pollution to a relatively clean, unpolluted area of the ocean. This points out the need to control how the water is collected even if it is clearly done in a non-polluted part of the ocean/sea. This is not a recommendation to not use NSW. Just a recommendation to be wary of what can go wrong that the average aquarist is unable to verify by home test kits.

Choose your source water and NSW with consideration to the purity you need; the cost; value; the environmental impact (wasted water); and exposure and risks to impurities.

What source water or water do you use for your marine tank water changes? Please post your experience and what you use.

[WillieM96]

I've been buying distilled water for my aquarium. Walmart sells 3 gallons for $1.65. Pretty good, I think- then again, I only have a 50 gallon tank.

[leebca]

That's a good price. When I travel I often don't buy bottled water to drink, I just buy distilled water. It's like 1/3 the price of drinking water.

So how much do you spend on water in a month? per year? You didn't mention the size or frequency of water changes, so I'm not sure what those $ amounts might be.

Thanks for posting, Willie.

[WillieM96]

I do 5 gallon water changes every 1-2 weeks plus about 2 gallons of top off every week. So, ballpark, I'm spending about $3.80 on water every week. I have a DI unit that I'll use occassionally but to me, it's worth the money to not have to deal with it.

[leebca]

I think I'd do it your way, until I get tired of carrying water home from the store. Thanks for sharing!

[jackryan]

May I kindly ask if subjecting NSW to both UV and Ozonizer after putting it under prolonged heat exposure (for example putting it in a sealed container inside the back hood of a car under the mid-day sun), and keeping it in storage for a few days without lights would help significantly managed down any other unwanted hitchhikers such as ich, righ?

Thanks in advance...

-JackRyan

[leebca]

The UV treatment will be the most valuable IF the energy of the UV and the flow through the UV (exposure to the UV) is properly controlled.

Still, in general, there is little fear in picking up problematic organisms if the NSW is coming from out at sea. If it is being collected at the shore, pollution is usually more of a concern than unwanted organisms. Still the UV combined with dark, is the conservative approach.

Different organisms have different heat tolerances, so the heating may help reduce problematic organisms, but not guaranteed to kill-off everyone of them.