Dr Joshua Waters is a non-canonical character created for the Agatha Christie's Marple adaptation By the Pricking of My Thumbs. He is the local doctor in the village of Farrell St Edmund where most of the action in the later part of the story takes place.
There is a Major Waters in the original novel who asks the local vicar of Sutton Chancellor to look for the grave of a child Lily Waters. However it turns out that Major Waters and Lily Waters in that story could be fictitious names. By contrast Dr Joshua Waters has a totally different backstory and plot role and so should be considered a different character despite the association of names.
Like many other villagers, Waters meets Miss Marple and Tuppence soon after their arrival in the village. He fills them in on the background to some of the personalities in the village, notably Sir Philip Starke. He tells them that Sir Phillip and his wife had a still-born child and his wide died soon after. This explains why Sir Phillip seems to dote on the children and young people in the village. Waters notes that Sir Phillip was very kind to his own daughter Rose when she was young.
Some effort is made to make Waters appear sinister. In one scene, he is shown asking Septimus Bligh (who had just seen Miss Marple and Tuppence) what the two women know. Septimus tells him they had a painting and the name on the gate is "Waterlily".
This is only explained in the later part of the story when Waters himself tells Miss Marple that besides Rose, he once had another daughter, Rose's twin Lily. When very young she disappeared and her body was found two weeks later. Waters's wife died of sorrow shortly thereafter. Like many villagers, Dr Waters thought Job Perry, who found the body, was also possibly the killer. Job was, according to Waters, a little "off kilter". The conversation between Waters and Septimus Bligh was perhaps nothing more than his curiosity about what really happened to his daughter.
Waters opposes his daughter Roses's relationship with an Amerian servicemen Chris Murphy and much prefers that she marries the local police constable Ethan Maxwell. Chris Murphy himself explains to Miss Marple later that this is only because Waters fears losing Rose who is all he has got. At the end of the episode, he is cheered to learn that Chris intends to settle down in the village after marrying Rose.
Dr Joshua Waters is portrayed by Michael Maloney.