Facebook needs to make sure the new tools it has introduced to help safeguard user data in the wake of the Cambridge Analytica scandal is done in "practice and not only on paper," the European Union's top data watchdog told CNBC.

The social network has unveiled a raft of new tools since news of the fiasco broke, with the aim of helping users understand and control how their data are used.

Giovanni Buttarelli, the European Data Protection Supervisor (EDPS), said Facebook CEO Mark Zuckerberg needs to ensure these changes are done in practice.

"I take note of what Zuckerberg has said recently, he said that he takes care of the privacy right. The question is they should do it in practice and not only on paper," Buttarelli told CNBC in a phone interview on Thursday.

Facebook revealed Wednesday that 87 million users were affected by the scandal which saw a quiz app scrape the data from profiles on the social network and pass them over to political consultancy Cambridge Analytica.

Buttarelli criticized social media firms' data collection practices.

"There are days when you have the impression people are treated as battery animals or experimental rats. We are treated as a farm for data. We are in within a walled garden and every single action is monitored," Buttarelli said.