If it is your waterline you want to cover with eyeliner, then all you will need is some mascara, black eye shadow, and some sort of slim brush or applicator. What you will want to do first is take the brush and dab a little mascara onto the end. Use the brush to swipe the mascara on your waterline like you would normally. Without blinking too much in between, use the brush to dab on the black shadow over the mascara to seal it in. If you need white eyeliner, you can use clear mascara or just skip right to the shadow part.
If you want to line your upper lash line then you only need the black eye shadow. Load up your brush with the shadow. Then lightly spritz everything on the brush with water. Reload your brush and then apply onto your eye like you normally would.
Using this technique is useful if you want multiple colors without buy lots if different liners. It saves money since you can use things you already have. Also, if you find an eye shadow you love, but wish it was a liner, problem solved.