Using DTH (down the hole hammer) drilling method

We are in the business of water wells drilling in Romania, Europe. In Romania the soil varies from non-cohesive to cohesive and hard rocks. How feasible it is to use DTH (down the hole hammer) technique in this situation for drilling? We want to learn more about the drilling with DTH and its benifits at our site perticularly for water wells. Can you give some information about the feasibility of DTH in different soil conditions, types of bit required and recomendation for casing types while using this technique. Help would be much appreciated. Best regards, Madalin Neagu SC FORMIN SA www.formin.ro