Wash and slice the jalapeños into rings approximately 2-3mm wide. Set aside.
Place the water, vinegar, sugar and salt into a saucepan. Stir to dissolve while bringing to the boil.
Add the sliced jalapeños and maintain a gentle boil for 3-4 minutes.
Turn off the heat and leave the jalapeños to steep in the liquid for 15 minutes, allowing them to soften slightly.
Spoon the jalapeños into sterilised jars then cover with the pickling liquid.
Allow to cool completely before sealing.
Store in a cool dark place. Once opened refrigerate and consume within 1 month.