I think that your problem is in the location of the image. You shall place it in your source, and then use it like this:
JButton button = new JButton();
try {
Image img = ImageIO.read(getClass().getResource("resources/water.bmp"));
button.setIcon(new ImageIcon(img));
} catch (Exception ex) {
System.out.println(ex);
}
In this example, it is assumed that image is in src/resources/ folder.