Begin by gathering your ingredients and a high-powered blender. Add a generous cup of fresh or frozen raspberries along with freshly squeezed lemon juice into the blender. Blend on high for about 30 seconds or until the mixture becomes silky smooth.

Place a fine mesh sieve over a clean bowl or pitcher to catch the raspberry seeds. Pour the blended raspberry-lemon mixture through the sieve, using a spatula to press down and extract as much liquid as possible.

In a large pitcher, pour the strained raspberry-lemon mixture. Add approximately four cups of cold water, adjusting the quantity based on your personal taste preference for tartness. Stir vigorously until well-mixed.

Refrigerate the mixture for at least 30 minutes to allow flavors to meld. Serve over ice in tall glasses, garnishing with fresh raspberries or lemon slices.