Typical contaminants are found in Well water:

Calcium
Magnesium
Iron
Manganese
Sodium
Sulphur
Aluminium
Ammonium
Phosphates
Nitrates
Nitrites
Chlorides
Pesticides

There are contaminants that can be in water that may or may not pose a risk to health, but nonetheless are undesireable.

Odours
Colour

While these do not directly have an effect on health, they can be very disruptive to normal life and can be tested for to determine their concentration. Odours are more difficult to test for as they often react with air and can be gone before the sample is opened for test. In the case of odours it is often necessary to observe this on site to determine how big a problem it really is.

Much more harmful are the following:

Cysts, such as Cryptosporidium
Viruses
Other biological contaminants.

These can all be treated to ensure the watersource is sterile and secure.

pH

A measure of the degree of alkalinity or acidity of a solution as measured on a scale of 0 to 14. The midpoint of 7 on the pH scale represents neutral, ie that the solution is neither alkaline nor acidic. The accepted range for domestic water is between 6.5 – 7.5.

The issue of pH is not so much that it is a health issue, more it is taken to indicate that if the water is outside of the accaptable range it will cause any metal fittings that it comes in contact to corrode and eventually every fitting and appliance will require change. The metal is eaten away and leaks and failures occur.