Are we drinking the same water that the dinosaurs drink?
Short answer, YES.
Professor Ken Carslaw from the University of Leeds explains the old water phenomena as follows,
"Water is recycled through the water cycle. It evaporates from the oceans, forms clouds, rains or snows, the rivers return it to the ocean.The longest timescale of water anywhere in the cycle is in the deep of the ocean and deep in the ground (perhaps 10,000 years). However, water is very slowly destroyed chemically in photosynthesis and recovered again in respiration. One can calculate how much water remains from the dinosaur age from the total amount of water on the planet and the amount of water taken up in photosynthesis per year.The Earth's plants take up 12,00 billion kg or water per year. The total water on Earth is about 1400 billion kg. So within about 100 million years most of the water will have been chemically destroyed. Dinosaurs lived 65 years ago. So, SOME of the water we drink is the same water but more than half is different water."