Combine the sauce ingredients in a bowl (don't include the water), rub over the meat.
4 tbsp balsamic vinegar, 2 tbsp Worcestershire sauce, 2 tbsp maple syrup, 1 tbsp English mustard, 1 tsp smoked paprika, 1 tsp thyme, 2 tsp oregano, salt and pepper
Place the pork fillet in the slow cooker, pour the water around the meat.
200 ml water, 0.5 kg pork fillet
Cook on low for 6-8 hours. At the end, transfer the pork fillet to an oven tray and bake for 15 mins in the oven (at 200℃ / 390℉) to crisp it up.
Notes
I cook this in an oval 3.5 litre slow cooker. If using a larger slow cooker this could cause the liquid to boil off more quickly and lead to the sauce burning onto the slow cooker pot.If you have a larger slow cooker, like 5.7 or 6.5 litre, then increase the water to 300 ml and check the dish regularly during the cooking time to look out for burning.It is always a good idea to check your dish during cooking whatever the size of slow cooker you have, because all slow cookers cook differently.