All natural or sparkling water is always permitted. Flavored water is doubtful.
San Benedetto – Rav Richetti
Levissima and San Pellegrino – Sparkling or non-sparkling, both kosher-le-Pesach
Ferrarelle spa, OU and IKU – Riardo (Caserta) – Ferrarelle OU
Natia OU
Uliveto OU – OU list
Rocchetta Brio Blu OU – Rocchetta Naturale OU
Paradiso – Rav Margalit – kosher le Pesach