When the hot tub is assembled correctly with all the staves in place, you can be sure that it will not be able to leak straight out between the staves. If it still leaks, it is because water is leaking through knots in the wood.
The pictures show how a knot can be corrected from the inside if necessary. To be sure no leakages will occur in for instance knots this section will show a way to quickly rectify potential leakages. It is best to do this procedure before starting the assembly.
But it is not necessary since healthy knots swell up quite fast, but for the person who wants a hot tub without any leakages at all this is a simple method to ensure that. Fill the knots with a mold resistant transparent silicone and even out with your finger tips. To remove excess silicone turpentine can be used.
Alternatively, the base has not been assembled correctly and there is leakage between the tongue & grooves joins, from there water can run into the groove where the staves and base are joined together.
As the base dries, any cracks left during assembly will become even larger.
Instructions with pictures show how this can most easily be fixed:
Here on page 4 it is explained how important it is to mount the bottom correctly.