I have been feeding my plants with each watering for a very long time now.
I only use pure water when the plants are in very small containers, because I need to water/feed 3 to 5 times a day, and even at a small dose, I want to avoid any salt buildup so I use plain water about once a week ‘till copious runoff. Otherwise, If the plants are in larger containers which do not need multiple waterings/feedings each day, I never use plain water.
I do the same for all of my non cannabis plants also.
The cannabis growing community is generally somewhat insular in their tendency to think that cannabis is a special needs, unique plant, which requires all sorts of cannabis specific products.
Newbies are particularly easy marks.