Composite H₂O 1₁₀–1₀₁, CO 10–9 and CO 3–2 spectra of Class 0 and Class I sources averaged in order to compare the line profiles of two types of sources. All spectra are rescaled to a common distance of 200 pc, shifted to the central 0 km s^-1 velocity, rebinned to a 0.3 km s^-1 velocity resolution. The CO spectra refer to a 20′′ beam, the H₂O spectra to a 40′′ beam. The red spectra overlaid on top of the ¹²CO 10–9 are obtained by normalizing all the spectra to a common peak temperature first and then averaging them.