Tomatoes need full sun.
If they are planted in the ground you can check them in the morning to see if they look wilty-if they do, water themat ground level-don't get the leaves wet or let water splash on the leaves (soil-born virus can be splashed onto the leaves). If the soil around the plant is dry beyond the second knuckle of your index finger water it. If the plant looks wilty in the late afternoon it's probably due to the sunny location and not a need for water. As plants get larger they will require more water, so a little transplant might only take a pint of water, a fruit-beaing sized plant could take two gallons every three or four days.