Water meniscus differences. Test tubes containing distilled water (left), tap water and sea water (right), showing their varying menisci. The meniscus is the curving of water at the surface due to its surface tension, the attraction of molecules for each other. The height of the menisci, where the water touches the sides of the test tubes, varies. In distilled water, which has no dissolved matter in it, the meniscus is small. Tap water, containing a few dissolved chemicals, has a slightly taller meniscus, and sea water has a much taller one. This is because dissolved salts can increase the surface tension of water.