Ideas for dealing with (or without really) buckets.
Large clay jar - holds 10 or 20L of any liquid, sealed, can not be used to craft from, used to transport liquids without a bucket or barrel - 2x2 or 3x2. Could be 2 sizes, 1 for 10L, 1 for 20L.
Large bowl - holds 5L of liquid only when in a container. Can not be removed with liquid in it. Can be used to craft from. 1x2
Small bowl - holds 2L of liquid, same restrictions as large. 1x1
Bowl can be made from clay or wood.