The only water that would be present would be waste following cleaning and that will be minimal, moreover clean downs will only be carried out during in gaps in production.
What happens to this waste water? Does it pool?
Reviewing clause 4.4.3 the wording suggests to me that it is possible to have a scenario where drains are not present, but only if there is no contamination risk i.e. splash hazard. From I.G for 4.4.3:
Drainage systems must not constitute a potential risk to product (e.g. from potential leakage) when passing through or over production areas. Where feasible, the design of equipment must ensure that process waste water(e.g. condensate drainage from refrigeration or temperature-controlled areas, or sink waste water) goes directly to a drain to minimise contamination risk.
Where significant amounts of water are used (e.g. where wet cleaning is carried out) and direct piping to a drain is not possible, floors must have adequate falls to cope with the flow of effluent (i.e. pooling of water should not occur) as this constitutes a splash hazard and, therefore, a contamination risk
I haven't experienced a facility without drains, but I anticipate a key part of the RA would regard the EMP and any contamination hazard from pooling fluid. Important not just to potentially satisfy the auditor but of course to protect the product if there is indeed a contamination issue already occurring.