In a medium saucepan, add quartered strawberries, filtered water, and granulated sugar. Heat over low, stirring until sugar dissolves, about 2–3 minutes. Increase heat to medium to bring to a low boil, about 2 minutes.

Reduce heat to low and simmer for 20 minutes, stirring frequently. Mash strawberries gently with a potato masher to enhance flavor release, thickening the mixture.

Remove from heat and let cool for 5-10 minutes to settle flavors.

Strain the mixture through a fine mesh sieve over a heat-proof bowl, pressing strawberries to extract juice.

Transfer syrup to a glass jar, allow to cool completely before sealing. Refrigerate and use within two weeks.