I have had a pain in my lower left back quadrant since yesterday. I'm wondering if I should start drinking something for my kidneys.

Wow, that's quite a stretch of diagnosis!
Feel free to drink all the healthy liquids you want. I drink a lot of very watered down (at least 4x more water) real juices, mostly grape.
But I'm sure that you are aware that the first thing a doctor is going to wonder about is simple muscle strain, and take it from there. Do you have history involving your kidneys? Keep in mind that we know absolutely nothing about you, whereas your doctor does!