OXYGEN
Not less than 4.0 mg/L for warm water habitats and 5.0 mg/L for cold water habitats.

CARBON DIOXIDE
Aquatic plants depend on CO2 for photosynthesis. Organic decomposition produces CO2 and reduces dissolved oxygen. Surface waters normally contain < 10 ppm of free CO2. Typically when the pH is 8 or greater there will be no free CO2 unless the input is greater that the ability of the gas to reach equilibrium with the CO2-Bacarbonate-Carbonete system.

TOTAL HARDNESS
Soft water = 0-50 mg/L.
Medium hard water = 50-120 mg/L.
Hard Water = 120-180 mg/l.
Very hard water = more than 180 mg/L.

CALCIUM
Limit of calcium hardness for drinking is 200 mg/L. Concentrations in water from limestone areas usually range from 30 to 100 mg/L.

MAGNESIUM
Limit for drinking is  150 mg/L.  In areas rich in igneous or carbonate rocks, magnesium concentrations usually range from 5 to 50 mg/L.

pH
Ranges from 5-9 are safe for fish under otherwise normal conditions.  Drinking water standard (EPA) = 6.5-8.5

ALKALINITY
Expected total alkalinities in nature usually range from 20 to 200 mg/L.

NITRATE - N
Average for unpolluted  fresh water is 0.3 mg/L. Concentrations in drinking water should not exceed 10 mg/L.  (EPA standard)

NITRITE - N
Maximum for drinking water is 1 mg/L. (EPA standard)

AMMONIA - N
Ammonia nitrogen is usually present in less than 1 mg/L in unpolluted well oxygenated water.  Concentrations may reach 5-10 mg/L in the anaerobic hypolimnion of a eutrophic lake.

PHOSPHATE (Orthophosphate)
Average for unpolluted fresh water is 0.1mg/L.

CHLORIDES
Maximum chlorides for drinking = 250 mg/L.  Chlorides usually average 20-60 mg/L.

IRON
Should not exceed 0.2 mg/L for domestic use.

SILICATE
Natural waters often contain 1-10 mg/L silica and rarely exceed 60 mg/L

SULFATE
Should not exceed 250 mg/L for drinking (EPA standard)

SULFIDES (hydrogen sulfide) Concentrations high enough to be a health risk also make the water unpalatable. Concentrations as low as 0.5 mg/L can add objectionable taste and a rotten egg odor to drinking water.

TDS
Total dissolved solids should not exceed 500 mg/L for drinking