Add the water and sugar to your saucepan and place it on the stove over medium-high heat.
Stir the mixture a few times as it heats up. Bring it to a boil.
After it comes to a boil, lower the heat to a simmer and let it simmer for 3 minutes.
Remove the saucepan from the heat. Cover it with a lid and let the mixture cool to room temperature.
Once the syrup is at room temperature, pour it from the saucepan into your storage container. Use a funnel if necessary.
Store the syrup in the refrigerator for 2-4 weeks. Discard at any sign of cloudiness or mold growth.
Microwave Method
Add the water and sugar to a heatproof, microwaveable container. Stir to combine.
Microwave the container for 30 seconds, then remove and stir the mixture.
Continue microwaving in 20 second intervals and then stirring until you can't see the sugar anymore.
Once the sugar is all dissolved, allow the mixture to cool to room temperature. Then transfer it to your storage container, if it's different from what you're microwaving in.
Store the syrup in the refrigerator for 2-4 weeks. Discard at any sign of cloudiness or mold growth.
Cold Method
Add the water and sugar to a sealable container or jar. Seal up the jar and shake it to mix.
Continue shaking for about 30 seconds, then rest and let the jar sit. Shake every now and then until you can't see the sugar anymore.
If you want this process to go faster, you can use a blender instead of shaking the mixture.
Once all the sugar is dissolved, transfer the syrup to your storage container, if it's different from what you're mixing in.
Store the syrup in the refrigerator for 2-4 weeks. Discard at any sign of cloudiness or mold growth.
If you are using the Cold Method, you might want to try to find superfine sugar (aka caster sugar) since it will dissolve faster in the water. You can make your own superfine sugar by running regular granulated sugar through the food processor.
With all methods, if the simple syrup is intended for cocktail use only, you can add an ounce of plain vodka to the syrup to make it last longer in the fridge. This will make the syrup have an ABV content of about 4%.