When it gets below 20 degrees and you have a crawl space under your house and no protection for your water pipes or just want to be cautious-try this: Open all your cabinet doors under sinks and let the faucets slowly drip. Put bowls under the faucets, that collects the water for later use, for watering plants, etc. We had our drains freeze once doing this, so I use the bowl method now. If the water runs over, it will go down the drain, but just check periodically and add new bowl.
When we did this & our pipes didn't freeze.