Hot water jug fixed ready alongside the sink.
I have a cold water tank (100litres in stainless steel) with water extracted by jiggling the lever on the tap above the sink. I do not, as of now, have a running hot water supply. I could fit a calorifier to use engine heat to warm up water - but that would only work when the engine has been running recently.
A simpler (low-tech) solution is to fit a large vacuum jug close to the sink and fill it up with hot/boiling water in the morning. It then stays hot all day. The jug has a pump action to get the water to pour out. I have had no problem with leakage while at sea, but placing the jug spout over the sink is a good safety feature.
Hot water jug fixed ready alongside the sink.