Briton Gillian Gibbons has been imprisoned for 15 days in Sudan - a country with some of the world's worst prisons, according to campaigners.
Omdurman prison is considered over-crowded and dirty
Justice Africa, a UK-based research group, said even a Sudanese person, used to the hardship of daily life, would find conditions hard.
A US State Department report described the jails as "harsh and overcrowded".
However, the Sudanese authorities have not confirmed where Mrs Gibbons will serve her sentence.
And observers point out that some categories of prisoners can receive preferential treatment.
The Sudanese authorities have frequently refused prison inspections by international agencies.
Mrs Gibbons was jailed for 15 days by a court in Khartoum for being guilty of insulting religion after naming a teddy bear Muhammad.
She was expected to spend her sentence at Omdurman, the largest women's prison in Sudan and usually full of women convicted of making and selling alcohol. But her lawyer said she was later moved for her own safety following protests.
Justice Africa's Sudan co-ordinator Hafiz Mohammed said guards at Sudan's prisons "treated inmates like slaves".
Mr Mohammed said there was a possibility Mrs Gibbons may be given special treatment, but said she will have "a very difficult time" in an institution without beds, clean drinking water and with such poor quality food that she'll be unlikely to eat it.
"Prisons are overcrowded, there are no roofs so most of the women have to use sheets to keep the sun off them.
"It's not divided into cells but just one large area with one wall surrounding them."
Mr Mohammed said Mrs Gibbons would find hygiene "very poor, and she won't be able to drink from the taps. She'll have to rely on bottled water and food brought to her."
Relatives of Sudanese inmates are allowed to bring food and water to the prison.
"But it's very difficult even for the Sudanese people who are used to living in the harsh conditions of the country."
According to the US State Department's report on human right practices, Sudan's prisons are "harsh and overcrowded".
The report from 2006 says: "Most prisons were old and poorly maintained, and many lacked basic facilities such as toilets or showers.
"Health care was primitive; prisoners usually relied on family or friends for food. Prison officials arbitrarily denied visits to prisoners."
But it pointed out: "High-ranking political prisoners reportedly often enjoyed better conditions than did other prisoners."
It also reported that security forces "routinely mistreated persons in custody.
"There were credible reports that security forces held detainees incommunicado; beat them; deprived them of food, water, and toilets; and forced them to sleep on cold floors."
War and poverty
The United Nations Mission in Sudan (UNMIS) said the overcrowding in Sudanese prisons was due to growth in population and crime while the prisons, built many years ago, have not expanded.
"The war and poverty have aggravated the situation. The prison population is growing mainly because of increase in crime and poverty caused by instability and other social and economic factors," a UNMIS report from 2004 said.
The poor conditions sometimes drove inmates to riot, although this was not very common, UNMIS said.