Yongah Hill Immigration Detention Centre, about an hour northeast of Perth, also limits support services and family visits, impacting the mental health of some detainees, according to a facility review.
"We identified several areas that are not satisfactory," Commonwealth National Preventive Mechanism Ombudsman Iain Anderson said on Monday.
The review in June found there was limited access for detainees held in the centre's high-security area to lines of communication and timely information.
A review of a detention centre has found some detainees have limited access to basic services. (Cortlan Bennett/AAP PHOTOS)
They also don't have the same access to facilities, programs and activities available to the general population compounds.
"We also had concerns with the use of a soft room being used as part of the high care accommodation," Mr Anderson said.
"In our view, this soft room meets the definition of a dry cell, the use of which is prohibited in the Immigration Detention Network."
The room lacks the basic amenities required to hold an individual for any length of time, including a toilet, sink and running water.
The watchdog recommended the Australian Border Force stop using the so-called soft room until it completes its work on safety guidelines, practices, and procedures were developed and implemented.
Improved access to lines of communication, information, programs and activities were also recommended.
About 160 people are detained at Yongah Hill Immigration Detention Centre, with 29 of these held at the facility for more than six years.
The centre is controlled by the ABF with detention and health services contracted to Serco Asia Pacific Pty Ltd and International Health and Medical Services.
The Refugee Council of Australia (RCOA) said it was deeply concerned by the findings about the room.
"The discovery of this unregulated space, which lacks basic amenities such as a toilet, sink and running water, is troubling and raises serious questions about the conditions detainees are subjected to," deputy chief executive Adama Kamara said.
She said it showed a disturbing disregard for the dignity and basic human rights of people in detention."The lack of checks and balances normally required for this type of space is glaringly omitted," Ms Kamara said.
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