Roller Coaster Tycoon how to build a waterslide?

First you must dig a hole for the water. Click on the shovel on the left of the screen. Click on the button with the mountain on it. Then a panel should pop up on the bottom left of your screen. Click the button with the arrow pointing down into a hole. Click the up or down arrows to change the size of it. Hold down the left mouse button until it's deep enough for you. Click on the shovel again, then the button with waves on it. Click in the hole where you want the water level to be. Hope this helps!