[mike31154]

It's a good idea to get informed as to the quality of your tap water if using it directly for your system. That's really the best way to determine what kind of filtration/treatment is appropriate for the water you're using for your system. I used tap water for close to two years and have experienced an improvement in my system since switching to RODI water just over a year ago. The TDS (total dissolved solids) in my tap water is typically around 210. I reviewed the documentation available from the regional district to see where my tap water comes from and what is in it. Most water suppliers, whether private or city/municipal will have this info available on line these days. I've heard that you folks on the coast, Vancouver etc. have very low TDS to start with from your source, something around 10. You can probably do without RO filtration with TDS that low quite easily, but it's still a good idea to find out what those TDS consist of. The thing about using RO water is that you're starting with a known element with virtually no contaminants when mixing up your salt water. Using tap, you never quite know what you're adding to your system that may contribute to undesireable consequences in the long term.

Find below a report on my local water from a few years ago. While it contains some good numbers for pH, calcium and a few other minerals beneficial to a salt water aquarium, there are traces of a lot of other stuff that I really don't want to take a chance on. The 1 micron poly pre filter on my RODI system gets gummed up substantially within a month or two of water changes. Another thing I've noticed since switching to RODI water is that my Alk is much lower than it used to be when using tap water, too low in fact, but my critters, especially GBTA have never looked better.

North Kalamalka Lake Intake Water Quality 2008
Water System: Greater Vernon Water
Source: Kalamalka Lake
Facility: Kal Lake Pumpstation
Sampling Point: Kal Lake Intake
Date: 7/14/2008
INORGANIC Results (mg/L unless noted)
Aluminum <0.050
Antimony <0.0030
Arsenic <0.0050
Barium 0.027
Boron 0.021
Cadmium <0.00010
Calcium 40.6
Chloride 5.38
Chromium <0.015
Copper <0.0030
Cyanide < 0.01
Fluoride 0.24
Iron <0.20
Lead <0.001
Magnesium 19.8
Manganese <0.0050
Mercury <0.00030
Molybdenum 0.005
Nitrate (as N) 0.069
Nitrite (as N) <0.010
Potassium 5.07
Selenium <0.0050
Sodium 18.4
Sulphate 51
Uranium 0.003
Zinc 0.011
PHYSICAL Results (mg/L unless noted)
Alkalinity (as CaCO3) 152
Colour <5 TCU
Conductivity 409 microS/cm
Hardness (as CaCO3) 183
pH 7.8
Total dissolved solids 238
Turbidity 1.0 NTU
UV Transmittance @254(%) 91%