蜻蜓点水 [- - diǎn shuǐ]like a dragonfly skimming the surface of the water — touch on sth. without going into it deeply; (as) a dragonfly skims the water surface; scratch the surface; touch superficially; use a light touch in writing as dragonfly skims water surface:
•¶ 做调查工作不能蜻蜓点水， 要深入实际。 To make an investigation one, should go into matters deeply, not just scratch the surface.