Rinsing with water after brushing is bad for your teeth - it washes away the protective fluoride from the toothpaste left behind after brushing. Fluoride toothpaste strengthens tooth enamel, making it more resistant to tooth decay and cavities. Fluoride also repairs weak spots. Spitting instead of rinsing ensures that the fluoride will be more effective, as the fluoride will remain on your teeth much longer than just for the two minutes that you are brushing.
You should brush your teeth with a pea-sized amount of toothpaste twice a day. The night brush just before bed is the most important. It allows your teeth to get the benefit of your fluoride toothpaste for many hours, if you don’t rinse, eat or drink after brushing.
Remember, have a drink BEFORE you brush your teeth, not after.