I read that I should stop watering my crops like lettuce 10 days before harvest. Is this true?

The suggestion to stop watering lettuce 10 days before harvest is ill-advised. Lettuce is a good example of vegetable plants’; need for water all the way through the growing cycle.

Water usage by growing lettuce plants actually increases every day right up to the harvest, and the only justification for withholding water – perhaps for a couple of days – would be to assure that harvesters have access, and muddy soil is not transferred to the plant upon harvesting. Two charts showing daily water requirements for lettuce are included at this location https://cals.arizona.edu/pubs/water/az1132.pdf