Around 1,000 people a day spend 50p to spend a penny at the Jubiloo on the South Bank - but planning permission for the structure expires in a month's time.
Healthmatic says that an average of just under 1,000 people a day have used the Jubiloo since it opened in 2012.
During 2016 the number of visitors exceeded 1,000 on 140 days, and the busiest day was 13 August 2016 when 1,755 people made use of the facilities.
Two staff are on duty at the Jubiloo during opening hours.
The structure was given planning permission to remain in place for five years and five months, and with the end of that period rapidly approaching, permission is being sought to keep the Jubiloo in place till 2022.
See 17/00971/VOC for details.