is this safe to use if you have well water?

Thank you for your inquiry! Preen Lawn Weed Control only penetrates the soil a few inches down. It will have no affect on your well water. This product is to be applied to a wet/moist lawn, no rain/watering for 24-48 hours, then after that time period a rain/watering should occur. It is then safe for humans/pets to enter the treated area once it has dried from the first watering.