A multiluminescent composite material, CDs@EuW–MOF, is synthesized by self‐assembling molecular building‐blocks in the presence of carbon dots (CDs). Using water soluble CDs within the growth media of a hydrophilic metal‐organic framework (MOF) enables the incorporation of the CDs within MOF pores through a one‐pot synthesis. The emission spectra obtained using a broad range of excitation wavelengths (295–400 nm) show multiple emissions including the Eu 3+ red emission and the dual‐color (blue and green) emissions of the CDs. The red emission intensity of Eu 3+ ions decreases in the presence of water molecules, leading to the ratiometric detection of water in methanol within a wide response range of 0–30 % (V/V). Due to the quenching effect on the CDs emission, this composite can also sense acetonitrile. The results demonstrate that using a molecular building‐block approach is an efficient route towards the design of multiluminescent functional materials.