In a large saucepan, combine the water, vinegar, sugar, thyme sprigs, garlic, peppercorns, crushed red pepper, mustard seeds and salt and bring to a boil. Simmer over low heat for 10 minutes. Remove from the heat and let cool for 5 minutes. In a wide heatproof bowl, cover the carrot slices with the pickling mixture. Let cool to room temperature.