You will often get a lot of ...

You will often get a lot of conflicting advice on how to treat a borehole.  The analysis is not optional but absolutely essential, not only for the bacterial content but the physiochemical content.  There may be metals in the water such as arsenic, which will require one form of treatment, there are boreholes containing iron or manganese, which will require oxidising prior to specialised filtration using green sand, base iron removal or fylox.  There may be suspended solids present which may be filtered, and the pH may need to be corrected if it is acidic.  Filtration may well help reduce any bacterial load in the water.  If there is a significant bacterial content, then it should be pre-filtered to assist in bacterial removal.  Dryden Aqua have produced a filtration media AFM, which works like sand but doesn't get colonised by bacteria.  UV is very good at reducing bacterial levels and will kill protozoa such as Giardia or Cryptosporidium (which should be pre-filtered first) but there is no residual effect so bacteria can grow in the water on storage.  If there is iron or manganese present then chlorination may be used as an oxidant, I haven't successfully used ozone, but there needs to be a reaction time between injection and filtration.  Chlorine is effective at controlling coliforms and many bacteria at relatively low levels on clean water.  The starting point is the analyses.  From there, you will know what needs removing.  It will also dictate how the water is treated and whether further treatment is required to control corrosion in the pipes.