There are a few things you can do to prevent your cucumber salad from becoming watery. Sprinkling some salt over the cucumbers and letting them sit for 10-15 minutes can help draw out excess water, then rinse them off and pat them dry before adding to your salad. Cutting the cucumbers into thin slices releases less water into the salad. Avoid dressing the salad too far in advance as the salt and acid in the dressing can cause the cucumbers to release more water. If you have leftovers, store the salad in an airtight container in the fridge, and drain any excess liquid that accumulates before serving.