It may depend on the ...

It may depend on the bacterial and suspended material load present in the well water.  A number of wells contain iron or manganese or toxic materials such as arsenic, which require a pre-oxidisation and filtration stage prior to final treatment.  Assuming that this is not the case, then, depending on the size and complexity of the plant, the chlorine can be dosed using hypochlorite.  This can be monitored using a specific chlorine sensor, which can be linked in to the chlorine dosing pump.  When using hypochlorite, it is normally purchased as a liquid of approximately 14% but will degrade on standing.  The longer it stands the weaker it becomes.  It breaks down naturally to sodium chloride and oxygen, which cause crystals to form in the tank, the dosing line and dosing pump.  This can result in the like blocking, so the correctly sized pump and type of pump is critical.  Normal impulse pumps accelerate this break down and generate oxygen bubbles, which cause an "air lock" in the line.  Either a pump with a de-gassing head or a peristaltic pump will over come this problem.  The storage tank should be kept in a cool place and, ideally, should be black GRP and at no time should stainless steel be used due to rapid corrosion.  

Chlorine gas can be used but the handling of the system provides risks, which needs special attention and for smaller systems is not really practical.

In very small systems, slow chlorine release tablets could be used.

There has been a tendency to recommend chlorine dioxide for water systems.  These systems are not simple because many require the use of two dosing pumps and a reaction chamber and they are certainly NOT maintenance free and I have experienced extreme acid conditions when one precursor ended up dosing without the other.