The user can manipulate water in every form possible, the basic three being liquid, solid and gas, as well as transform it from one phase to another. More powerful users can convert water into the fourth phase, plasma.
The user can also manipulate every property of water, such as viscosity and density of water, changing liquid into thick and adhesive or thin as oil, or condensing vapor particles and liquid enough to be tangible to the point of solid and hardened.
Because blood cells is 55% blood plasma, which in turn is up to 95% water, advanced user can control blood via that water content, controlling the target by it, and even crystallize or evaporate it. This would take delicate control, as the blood plasma does contain other components.
Hama (Avatar: The Last Airbender) is one of the most powerful waterbenders, and can control water in all its forms, such as extracting water from plants and thin air. She can even control bodily fluids in the human body.
Katara (Avatar: The Last Airbender) is a powerful waterbending master, and can control water in all three phases, such as extracting water from plants and thin air and can even control bodily fluids in the human body.
Yukihina (Code:Breaker) using his Shape of Water ability to control his own blood by vaporizing it, and then injecting into Heike and freezing it from inside Heike's body.
Tokiya Mikagami (Flame of Recca) wielding Ensui, a sword that gathers water molecules and can control it in any of its three phases, making it a very versatile weapon.
Genbu (Magic User Kurohime) is the Water Spirit King, and can control water of all three phases, allowing anyone who subjugated him to control the water element magic to the highest level.
Saiyuki (Magic User Kurohime) gains Genbu's power by subjugating him, and she can freely shift between liquid, ice and vapor forms as a result.
Yuki-Onna (Magic User Kurohime) is a Goddess who controls snow and ice, freezing water into such, as well as shifting opposing ice-based attacks into harmless water.
Storm (Marvel Comics) can control the weather at tremendous levels, and can therefore manipulate water content within the air as precipitation, humidity and moisture.