Make the strawberry syrup. In a small pot on medium heat, mix the strawberries, sugar, and water. Wait for it to boil, then lower the heat. Mash the strawberries with a fork or potato masher while they soften.
Simmer. Let it simmer for 1-3 minutes until the strawberries are fully softened and the syrup has thickened a bit. Then, take it off the heat and let it cool down a bit.
Steep the basil. Put the basil leaves into the hot syrup and make sure they are fully covered. Leave the mixture for at least 15 minutes so that the basil flavor can become stronger. Take out the basil leaves and throw them away.
Mix and chill. Get a big pitcher and mix together the strawberry basil syrup (including the fruit bits), lemon juice, and water. Stir everything well. Put the pitcher in the fridge and let the lemonade chill for approximately 1 hour until it's completely cool.
Serve. Put some ice in glasses and pour the chilled lemonade. To make it look fancier, you can add a lemon wedge, a fresh basil leaf, and a slice of strawberry on top.