The Puddleman by Raymond Briggs
Tom refers to his grandfather as 'Collar' because he drags him around on a lead. One day, Tom decides that he will take Collar on a walk to see the puddles he has named after the members of the family, but the puddles are not there. Collar insists that this is because it hasn't rained, but Tom believes that it's just because they haven't been put in yet. He wanders off, leaving Collar talking to Mrs Whitebobblehat, and comes across just the person he needs ...Finally, puddles restored to their full, family-resembling glory, Tom and Collar go home for tea.