Combine the water, vinegar and sugar in a large heavy-based saucepan and stir over low heat for 3 minutes or until sugar dissolves. Increase heat to medium and bring to the boil. Boil, uncovered, for 5 minutes. Remove from heat and set aside for 5 minutes to cool.
Place the chillies, garlic and galangal in the bowl of a food processor. Briefly process until coarsely chopped and combined. Add the vinegar mixture and process until well combined.
Transfer to a clean, large heavy-based saucepan and stir over low heat for 5 minutes or until hot. Increase heat to medium-high and bring to the boil. Boil, uncovered, for 30 minutes or until sauce thickens slightly. Remove from heat and set aside for 30 minutes to cool. Transfer to an airtight container and use as desired.
Notes & tips:
This chilli sauce will keep in an airtight container in the fridge for up to 4 days. Serve it as a dipping sauce with roast sweet potato (kumara), pumpkin and potato wedges, drizzle over steamed Asian greens, serve with chargrilled salmon and prawns or roasted chicken, or use in salad dressings and sauces.