"Not happy with delay in giving my dad food and drink"

My dad had cancer and he was told not to have any food or fluids for 24 hours before he had a biopsy. He had his biopsy very late in the day and when he returned to the ward he asked for some fluid, as his mouth was extremely dry. The nurse stated that he couldn't have any fluid, as he had "nil by mouth" on his bed chart. We explained that he had nothing to eat or drink for 36 hours now and he had had his operation. The nurse disappeared and came back with the same answer. We were disgusted but thought that being in a hospital - "they know best". When the doctor visited my dad the next morning he asked if everything was ok and we told him that by this time my dad had not had anything to eat or drink for 2 days. He seemed shocked by this and stated that my dad should be having food and as much fluid as possible to keep his strength up. I am disgusted with this hospital. This is not the only bad experience that we have had with the hospital.