Juud
Two comments:
1. In the first column in the MEL extract it says:
30-1 Lavatory Toilet C
I interpret the C as the repair interval, and normally C would be 10 days
2. From the BA B747-400 MEL for Waste Systems
OPERATIONS (O)
Under EU regulations, British Airways aircraft are considered to be food premises and therefore have to have an adequate supply of hot and/or cold water available on-board whenever the aircraft is operating. This can be achieved by the provision of bottled water.
Hope that helps