Painting water and reflections in any medium often requires an understanding of the principles and properties of refraction, color theory, perspective, how objects sit in and on water and the shapes they thus create, and so much more. Painting them in watercolor requires layering washes. Here’s an example of painting simply water with no reflections.
A white or pale subject benefits from a background that contrasts in value. But first, lay in its palest shadows and colors as shown. This subject, a mute swan (Cygnus olor), has a bright orange beak. But the background water’s blue pigment may cover the beak shape because it makes painting the large background shape easier. Remove the (damp) pigment easily with a clean, damp brush after quickly painting the first background layer:
Dry the paper thoroughly before adding more shadow definition to the wings and body and a yellowish hue to the bird’s head and neck feathers:
Now add another layer of the same color just as quickly as the initial background wash to suggest waves and ripples.
Paint the bright orange beak in a creamy consistency, then add the black details when all is dry.
(Color appears a bit different here because lighting conditions weren’t the same.) I added yet another layer to the background water but did not suggest any reflections, which more or less disappear in choppy water because light is refracted in many directions. Obviously they’d be more dramatic on a smooth surface, as seen below in my painting Peaceful Preening, which is discussed in my book White! Light! Bright! How to Make Your Backgrounds Support and Enhance Your Watercolor Paintings.