how can i fix my Rover 45 diesel?

I drove my Rover 45 diesel (2004) too fast through standing water which promptly made its way into the air filter and the car would not start, i removed the air filter to get the car home and replaced the filter the next day BUT now the car seems to have no power to pull away and loses power on hills it is best described as gutless although when the turbo comes in it is fine but that seems to be coming in further up the rev range than before.