Vampires Vs. Aliens, Book One — Keith B. Darrell

A moonlit night, a young couple strolling hand-in-hand along a deserted country road. It seems like a perfect date night until he leans over to kiss her and instead sinks his fangs into her throat. The vampire drains his prey, sating his hunger, and releases the lifeless corpse. He wipes the blood from his lips, content to leave her body in the field to be found in the morning by the humans. He's momentarily blinded by a harsh light from above. He feels a vibration around him, a powerful wind, and a tremor in the ground. He opens his eyes and sees a spaceship has landed.
The aliens notice the vampire. They're confused because their sensors indicated there were no life forms in the area. But their sensors are calibrated for humans and other life forms... Not the undead.

The vampire learns that the aliens are setting up secret plants in isolated areas with the ultimate goal of stealing the Earth's water, a scarce but necessary resource they need to survive. Escaping from the aliens, he warns other vampires of the arrival of the aliens and their plans which, if carried to fruition, would doom the human race... And with no humans or other life left on earth, the planet's furtive vampire population would be deprived of its sole food source. Now the vampires must wage a secret war against the invaders while keeping the fact of their own existence from the humans, just as the aliens don't wish for the humans to learn of their invasion that's already underway.