Communication about water-induced hazards (such as floods, droughts or levee breaches) is important, in order to keep their impact as low as possible. However, sometimes the boundary between specialized and non-specialized language can be vague. Therefore, a close scrutiny of the use of hydrological vocabulary by both experts and laypeople is necessary. In this study, we compare the expert and layperson definitions of 22 common terms and pictures related to water and water hazards, to see where misunderstandings might arise both in text and pictures. Our primary objective is to analyze the degree of agreement between experts and laypeople in their definition of the used terms. In this way, we hope to contribute to improving the communication between these groups in the future. Our study was based on a survey completed by 34 experts and 119 laypeople. Especially concerning the definition of words related to water there are some profound differences between experts and laypeople: words like "river" and "river basin" turn out to have a thoroughly different interpretation between the two groups. Concerning the pictures, there is much more agreement between the groups.