Should I use filtered water or bottled water for espresso?

Neither tap water nor straight distilled water is ideal. The most practical options are: (1) a dedicated in-line water filter or Brita-style pitcher for medium-hard tap water, (2) mixing distilled water with a mineral packet (Third Wave Water is popular), or (3) using a low-TDS bottled spring water. Avoid using softened water (it replaces calcium with sodium, which tastes bad in coffee and can still damage machines). Test your tap water's TDS first — it might already be acceptable.