I do
commercial water testing in my lab, and have done a fair amount of field
research over the years.
Why do you think you need to test your water? Do you fill
tanks from questionable sources? A few
commercial boats will send me samples once a season to check their
tanks. But most people rely on
cleaning the system once a year and maybe adding a bit of chlorine when filling them. Not long ago, I set up an on-site water quality program for a company that operates
oil rigs. They get water delivered by a lot of independent supply boats, and can't take a chance that someone has saved a few bucks by topping off a tank from a polluted creek or with sea water. And it's not really practical for them to mail samples anywhere from
remote locations in
Asia. But that's a pretty unusual situation.
A good quality multi-function meter is going to cost about $1000, plus some
equipment to calibrate it. Most probes last for a year or two. Conductivity (salinity) probes should last a long time though. I do have a few pocket dip meters, like those referenced above, for field kits. I paid a lot more than $20 for them, though! They are not particularly accurate, but probably close enough for casual use. The biggest problem I have with them is that they burn through expensive button
batteries like popcorn. (Partly because the "on" button seems to inevitably get squeezed in my backpack.) I'd expect them to last for a year or two - just like a pH probe - if carefully stored in the proper solution.
BTW: These meters don't
really measure salinity or total dissolved solids. They measure
electrical conductivity and multiply the result by a fudge factor using the assumption that you have a certain solution of a pure
salt (usually either sodium chloride or calcium carbonate) sometimes with corrections for temperature and pH. Since this never happens in the real world, the result can commonly be off by as much as a factor of two. But you probably don't care because you just want to know
salty or
not too salty.
There are a few relatively simple kits that can give you an overnight E. coli and Total Coliform count. But the drawback is that you need a) a reliable
freezer to store the reagents and b) a 35C (body temperature) incubator. Possibly also a source of vacuum for the more accurate membrane-filter kits, though a hand
pump, such as those sold for bleeding brake lines, will do. This is going to end up costing you something like $10 a test, compared to sending to a lab for $25 to $50. Not counting
equipment costs.
Some outfits sell pre-made test kits that are supposed give you a pass/fail for total coliform bacteria. (Almost none of them describe the test correctly, suggesting that they don't even know what they are selling.) These usually look like a bottle half-filled with a purple liquid. You fill it up with your water and turns yellow after a day or two, if the water is contaminated.
These are almost useless. They produce a lot of false-positive results (for various reasons) and if they aren't incubated at the proper temperature for the proper time (did you buy that incubator?) they can give false-negatives too.
Bottom line: an inexpensive conductivity meter might be worth carrying, especially if you need to check the operation of your RO system. I would rely more on prevention for the rest.
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