Here is the simple way to create a water drop effect with the brush tool and layer styles:

1) To begin, create a new document in Photoshop of 512 by 512 pixels with a transparent background. Fill the layer with the pattern “wood”. 

2) Create a new layer and press D to go find the original color. In the Photoshop tools, take the brush tool (B). Change the tool settings by choosing a hardness of 100% and a diameter to 19 px.

3) With the brush tool in hand (B), draw a simple dot on the layer (the top) like this:

4) Reduce the opacity of the background to 3%. The black dot you just created will become almost transparent.

5) Now let’s play with the layer styles: start by putting a drop shadow opacity 100%, with a 90 degree angle, distance and size of 1px each. Set the overall lighting

Add an Inner Shadow, a blend mode to “product”, set the opacity to 43% the size to 10 px and the distance to 5 px.

Add a black inner glow, with the blending mode to “overlay” and a 30% opacity.

Let’s continue with beveling. In “technical”, set to “marked chiseling” 250% depth, size 15 px, 10 px blur. In “mode in your clear,” set a 100% opacity and shading mode, choose “color density, color and white opacity 37%.

The layer style is now finished! By clicking on “new style” in the layer style window you can save. This will allow you to use it for text or other uses.

6) To complete this project, you are free to create other drops with a smaller or larger diameter.

For a gradient effect, you can add a layer between the bottom and drops. Take the gradient tool with black to transparent and from top to bottom. Reduce the opacity to 50%.

Your water drop effect is created!