You're likely to get this at some point just by playing, but if you want to hunt it down instead head to a free play game from the main menu and select any map, i'm not sure if wet weather cleans your car so best to choose a level such as Kortatti lakes and play in the afternoon, change the weather with X on the level select second screen. Drive around for around 10-13 minutes, avoid landing in water or going through a car wash, after driving around for that amount of time you should get the achievement, might be a little shorter or longer but eventually it will pop.
get 2 achievements in one with this below video guide.
video guide -