A team from the Healthcare Environment Inspectorate visited Western Infirmary in Glasgow in August and found that there was no time-scale in place yet for when a Legionella policy will be implemented.
Inspectors were told on a previous visit to the hospital in 2011 that NHS Greater Glasgow and Clyde's policy for Legionella, the bacteria that causes Legionnaires' disease, was under review and due to be approved.
Minutes from a July meeting showed "no decision had been made on when the draft policy will be approved", the inspectors said.
The health board has a month to provide a time-scale for when a Legionella policy will be implemented.
Overall, NHS Greater Glasgow and Clyde is making good progress on standards to protect patients, staff and visitors from the risks of catching an hospital infection, according to the inspectors.
"Staff demonstrated good awareness, knowledge and understanding of their roles and responsibilities for infection prevention and control, and patient equipment was clean. However, there are a number of areas for improvement including two requirements that have not been met from our previous inspection," chief inspector Susan Brimelow said.
Rory Farrelly, the health board's acute director of nursing, said: "Clearly we need to reinforce some of our policies with staff, including the disposal of sharps, storage of linen and our Legionella policy which, like all our policies, is available to staff on our intranet."