Well, we know they did. They even had soap!

• u/sunagainstgold covers the topic of bathing in the Late Middle Ages, and I especially commend the first sentence of her answer;
• u/BRIStoneman covers the same matter, but for the Early Medieval era;
• and u/Somecrazynerd examines bathing and attitudes to hygiene in a general Medieval sense.

Mind you, the presence of the painting can be a helpful visual aid to anyone still unconvinced, but there's quite the wealth of information out there on bathing in the Middle Ages.