The Competition & Markets Authority (CMA) said it was considering whether Danone's deal to acquire a majority stake would result in a “substantial lessening of competition” within the market.
The CMA invited comments on the proposed acquisition and is now due to give a decision by July 6.
The deal - made for an undisclosed sum - was announced in February and would see Harrogate Spring Water join brands Evian and Volvic under Danone’s portfolio.
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Harrogate Spring Water is Britain's oldest bottled water and achieved sales of £21.6million in the financial year to March 2019.
Its current shareholders, the Cain family, will continue to hold a minority stake under the deal.
Managing director James Cain will join the management team of Danone Waters UK and continue to lead the Harrogate Spring Water business.
A statement from Danone said: "On 26th February, Danone and Harrogate Water announced a share purchase agreement under which Danone will (through a UK subsidiary) acquire a majority stake in Harrogate Water Brands.
"At that time, Danone and Harrogate Water jointly and voluntarily decided to refer the agreement to the Competition and Market Authority, demonstrating responsibility towards ensuring that the transaction happened in the right way for the UK marketplace.
"The transaction will be completed subject to regulatory approval from the CMA, following their review."
By Jacob Webster, Local Democracy Reporter
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