It's not
quite that simple. Most people who reduce/eliminate meat consumption are going to substitute something else rather than eat less, and what they substitute may be just as water intensive as the meat they replace.
For example, if a person's meat diet is virtually all chicken (reasonable given prices lately), substituting the chicken for almonds is a net neutral change. Almonds use every bit as much water as chickens do.
Granted, that may be an extreme example, as almonds are one of the more water-intensive crops, and chicken is one of the most water-efficient meats. There will likely be decent water savings in many cases, but at the very least, anything a person substitutes for their existing meat diet is going to use some water as well.