In-game, open the Shop , navigate to Construction > Buildings > Tools (or the Placeables category), and select the Waterstation.
Download the .zip file and move it into your game's Mods folder (usually located in Documents\My Games\FarmingSimulator[Year]\mods ). PLACEABLE WATERSTATION V3
If you're running a massive farm, place multiple stations near your furthest fields to minimize travel time for your water tankers. In-game, open the Shop , navigate to Construction