I think seven gallons is very conservative! My tomatoes are planted both in a pot and in the ground. I have to water the pot a bit more as it dries out faster. But with the rain we have been having, I think I used about a gallon or so last week and none so far this week.
My planter with my flowers is under an overhang and awning of our house and does not get rainwater! Very frustrating! I use a hose and sprayer and water every other day. DH is going to put mulch down to help keep in the moisture even more. I estimate 3-5 gallons every other day. I have 2 pots of flowers on my front porch. They are brimming with water from our recent rains so I haven't watered them either in a while but I use a gallon jug and give them each 1/2 a gallon every day or so in dry weather.
We have a sprinkler system with a rain sensor. It hasn't been on in over 2 weeks. Even with our 100 degree temps, we have had enough morning or night showers that it does not turn on. This will change I'm sure. The rain can't last forever here!
Some tips: water in the very early morning or after dusk as there is less evaporation from the hot sun and the ground/pots absorb and keep more moisture. When we do have our sprinklers run, it's at 5:30 in the morning. Or DH manually turns them on after 8:30 at night. I tend to water my plants at night, too or at least when the yard is in the shade.