The phrase "water down" is an idiomatic expression with multiple meanings depending on the context. Here are a few common uses and their meanings: Dilute the strength or intensity: This usage often refers to reducing the potency or impact of something, usually a concept, idea, or statement. For example: "The company watered down the original proposal to make it more acceptable to the shareholders." "The politician's speech was watered down to avoid controversy." Weaken or diminish the quality: It can refer to reducing the effectiveness, impact, or importance of something. For instance: "The revisions to the book watered down the author's original message." "The director felt that the studio's interference watered down the artistic vision of the film." Make a liquid less concentrated: In a literal sense, it means to add water to a drink or solution to reduce its concentration. For example: "The bartender watered down the whiskey to make it less strong." "The recipe called for watering down the sauce to achieve a milder flavor." In summary, "water down" is used to describe the act of reducing the strength, intensity, quality, or concentration of something, whether it's a concept, idea, statement, message, or even a liquid. The exact meaning will depend on the context in which it is used.

The previous answer is correct about the meaning, but there is another point that's important. It's a separable phrasal verb; so if you use a pronoun as the object, it needs to go between the verb and the particle. He watered down the sample. He watered it down.

The meaning is the same as weaken