"It's Supposed to be Thicker than Water" is the twenty-second episode of the 1969 ITC British television series Randall and Hopkirk (Deceased) starring Mike Pratt, Kenneth Cope and Annette Andre.

The episode was first broadcast on 13 February 1970 on the ITV.

It was directed by Leslie Norman.

Jeff (Mike Pratt) is hired to perform the seemingly simple task of delivering an envelope to an escaped convict - but doesn't know what the envelope contains.

Although the 22nd episode in the series, It's Supposed to be Thicker than Water was the 8th episode to be shot, filmed between September and October 1968.