As two young women arrested in Peru on suspicion of cocaine trafficking face a potential three years in prison awaiting trial, Prisoners Abroad warned overcrowding is at such critical levels inmates' face serious health dangers.
If sentenced to prison, Melissa Reid, 19, of Scotland, and Michaella McCollum Connolly, 20, who has an Irish passport, could face years behind bars.
"People often have to sleep on floors, in corridors, or even in the toilet areas," a spokesman said.
"The diet is extremely poor. Without being able to buy other food to supplement their diet people are lost. Clean water is a rarity and has to be purchased, often at inflated prices.
"Because of the overcrowding, infectious diseases such as tuberculosis and HIV are constant concerns."
Peru's prison system is at 200% capacity.
Medication is not provided for chronic or critical conditions, and medical treatments are generally paid for by prisoners or their families.
Prisoners Abroad, which sends survival grants to Britons held in Peru, warned medical concerns and isolation make time in a Peruvian prison "hugely distressing".
The group, which does not comment on individual cases, said the experience is particularly harrowing for inmates who do not speak the language.
Meanwhile, legal expert Bruno Min said Ms McCollum Connolly and Ms Reid may have the possibility of seeing their jail term out in Britain eventually.
