We have both but there is quite a distance between then - also the septic tank is about 3m deep and the well is 56m deep.

Our septic is ancient and is basically a hole in the ground - the new septics are 3 chambers and have a biological filter so the water from it is not raw sewage.

How close are you thinking of? You need to be aware of potential contamination but if things are properly constructed and meet the required legislation you should be ok.

Nigel