Lime & mint
Swap lemon for fresh lime and be generous with the mint.

Bright lemon, creamy coconut and a colour that looks almost tropical before you've tasted it.
Cold drinks
Bright lemon, coconut and an almost impossible tropical blue.
If your coconut water is already quite sweet, go easy on the syrup. Taste it first.
This is one recipe where the colour itself can be part of the fun.
Blue spirulina and lemon don't produce exactly the same blue you'd get in plain water or milk. Depending on how much lemon you use, the finished drink can land anywhere from a brilliant aquatic blue to turquoise.
Don't fight it. Make the lemonade taste good first, then adjust the amount of blue spirulina until you have a colour you like.
If you want to play with the effect, make the blue coconut base first and add the lemon at the end. You'll be able to see the drink change as the citrus mixes through it.
Replace the cold water with soda water and add it right at the end.
For a bar version, build the coconut, lemon and blue spirulina base first, pour it over ice, and top with soda. A tall clear glass does most of the work for you.
If it looks greener or more turquoise than you expected, don't immediately add more powder. The lemon itself is affecting what you're seeing.
If you want a cleaner blue, try reducing the lemon slightly, increasing the coconut-water portion, or using the citrus as a separate layer added at service.
If you simply like the turquoise colour you've got, leave it alone.
Swap lemon for fresh lime and be generous with the mint.
Replace some of the coconut water with pineapple juice. Expect the yellow juice to change the finished colour, which can be part of the point.
Blend the finished lemonade with plenty of ice for a blue coconut slush.
Use the lemonade as a base for a highball or spritz. Keep darker spirits and syrups light if you want the blue to remain the visual focus.
For approximately 1 litre, start with:
Make the lemonade first and taste it. Then add the blue spirulina gradually until you like the colour.
Keep it refrigerated and make it according to the same food-safety and holding practices you'd use for any other fresh lemonade.
If you're developing a packaged drink intended for longer storage, that's a different job: test the finished formulation for colour stability over its intended shelf life rather than assuming a cafe recipe will behave the same way.

Blue spirulina powder
Choose a pack