Add baking soda and citric acid to a glass (or ceramic) mixing bowl. Stir.
Add 80-90 drops of essential oil and stir until the essential oil is thoroughly mixed in.
Spray the mixture with water until you reach the desired consistency. The mixture should hold its shape when squeezed in your hand. While it may not come together in the mixing bowl, if it holds its shape when squeezed, you're ready to proceed.
Scoop the mixture into your silicone mold and firmly press it into the mold with the back of your spoon.
Allow the toilet bombs to harden for 6-8 hours (or overnight). Dry times may vary depending on temperature, humidity, and the size of your mold.
When dry, pop the toilet bombs out of your mold and store in an airtight container.
To use, add 2 toilet bombs to the toilet bowl and close the lid. Allow the toilet bomb to dissolve (approximately 20 minutes) and flush.