Here's the key thing: The number of babies a water spider can have depends entirely on how many eggs she lays in that sac.
Unfortunately, there isn't a fixed number! The size of the egg sac and the number of eggs it contains can vary quite a bit depending on factors like:
* The individual spider's size and health: Larger, healthier spiders might lay more eggs.
* Environmental conditions: Abundant food and favorable temperatures could influence egg production.
So, while we can't say exactly how many babies a water spider can have, we know that it's determined by the number of eggs in her egg sac.