It is believed the incident was caused by the wrong chemical being added to drinking water.
Image source, PA MediaBritish sailors have needed hospital treatment after problems with water supplies on board their warship.
Submarine hunter HMS Portland returned to its home base of Portsmouth on Friday after the incident.
A Royal Navy spokesman said it was a “precautionary measure” after an issue with the ship’s fresh water systems.
They said measures were being taken to “safeguard the ship’s company” during an investigation, with HMS Richmond asked to provide cover if needed.
HMS Portland spent much of last year patrolling UK waters and last July co-operated with Nato allies on a submarine-hunting exercise in the North Atlantic.
It helped track two Russian submarines as they sailed into the North Sea along the Norwegian coast.
Last month it tracked a Russian warship as it sailed in international waters close to the UK.
The Type 23 frigate was commissioned in 2001 and over the years has been used in anti-drug missions in the Caribbean (2007) and deployed against pirates off the Horn of Africa (2009).
The ship also helped with disaster relief in Belize after Hurricane Dean in 2007.
It underwent a lengthy refit in 2021 which included an overhaul of machinery, computers and IT systems.