Physical Properties: pH, electrical conductivity, alkalinity, and hardness
The pH of pure water (which is never really found in nature) is 7, and this is called “neutral” pH. If the pH value
is below 7, the water is acid, and if it is above 7, it‘s alkaline. Depending on where you live, water in your area
may be acidic or alkaline. Usually, mildly acidic or mildly alkaline water is not a health problem. However,
acidic water can cause corrosion of metal plumbing (see “metals”) and alkaline water is usually rather hard
(see “hardness”). If your soils are poorly buffered, the pH of irrigation water can also affect which plants will
What to do?
If you decide that your water is too acidic, an acid-neutralizing device is required to treat it. If it is too alkaline,
a water softener will usually correct the problem. Acid addition devices are sometimes used for irrigation
Total Dissolved Solids
TDS is a measurement of the salts dissolved in your water. Excessive TDS may indicate very hard water or con-
tamination with salt water, especially if chloride and sodium levels are also high. Plants may not be able to
grow with TDS above 1400 ppm. We measure TDS by both electrical conductivity and by adding up the
results of the other tests. Usually the two estimates are not exactly the same, but they should be somewhat
What to do about it?
High TDS can be reduced by reverse-osmosis systems, though they are expensive and can waste a lot of
Water hardness is caused by the minerals dissolved in your water. (In fact, this number comes from adding up
the results of the cations test.) If water is too “hard,” there will be mineral deposits in plumbing, cleaning
agents may not work well, and unpleasant tastes may be present.
What to do?
A water softener can be used to remove magnesium and calcium, and replace them with less troublesome
This is a measurement of the carbonate content of your water. It is usually not of concern for drinking water
unless it gets close to 400 ppm, in which case a bitter taste may result.
Water with low alkalinity is “poorly buffered” and not able to resist changes in pH. Water with alkalinity over
about 100 ppm can change the pH of your soil, if used for irrigation. If you use high-alkalinity water for irriga-
tion, you should use less lime in preparing your soil, and may need to make other adjustments. Excess alkalini-
ty can be treated with acid-addition systems, if needed for irrigation.
Note: By convention, alkalinity is reported as the equivalent amount of calcium carbonate, but in some
waters - especially if a water softener is installed - it is actually sodium carbonate or some other salt.