I try to water once once a week but I fail sometimes. And we have a rubber tree in our conservatory that needs watering far more often than this! I quite often sit there looking at it, thinking "I should be watering you!" then get up to do it and on the way to the kitchen get distracted and forget. Our other plants seem to thrive on neglect (carefully chosen you might say....).
We only have outdoor plants. I get my husband to water these once every 1 or 2 months, hoping it's going to rain in the meantime! They really only need watering in the summer.as they seem to survive the rest of the time.