I agree with Igor. Start with ...

I agree with Igor. Start with EPANET. Some consultants offer programmes with more bells and whistles and capability to transfer data between your mains records systems. A good basic grounding with awareness of what the programme is telling you and your ability to assess whether it is believable is essential. Many people can fall into the trap of believing everything the model does - it is only a tool and an extension of your intellectual capability so see it as such. Hope this helps and good luck - it's a very rewarding journey to become a competent modeller.