How are alcohols related structurally to water?

Alcohols are structurally related to water through the presence of the hydroxyl group (—OH). In fact, an alcohol can be viewed as a water molecule in which one hydrogen atom has been replaced by an alkyl group.12

Both water and alcohols feature an $s{p}^3$ hybridized, tetrahedral oxygen atom that holds two nonbonding pairs of electrons. However, because alkyl groups are bulkier than the hydrogen atom found in water, the R—O—H bond angle in alcohols is typically larger than the 104.5° H—O—H bond angle observed in water. For instance, methanol exhibits a bond angle of 108.9°.1

This structural similarity is responsible for many shared properties. The hydroxyl group is highly polar and capable of forming hydrogen bonds, which allows alcohols to interact with water molecules and explains why many lower-molecular-weight alcohols are miscible with water.23