Is there anything that I should put into my water,so the seeds will not dampen off?
You can try adding a fungicide. Make sure that all your materials are clean. If you are reusing containers/trays wash them with a bleach solution. Use a sterilized seed starting mix or make your own from bagged ingredients and make sure it doesn't get too damp. Good air circulation is also a must. A small fan on a low setting works well. Even with all that I still occasionally have seedlings damp off but only the ones I start inside or in the greenhouse. Seeds that I start in containers outside never seem to suffer. Too bad I'm in zone 7 and have to start some seeds under glass : ( If you look through the forums (starting from seed, insect & disease and some of the others) you will find more info. Good luck.