This is just fine! This is more or less how starter was made before the written word.
This will probably work great if you live where "wild" yeast is present. Some of us, though, don't have much yeast (if any) in our kitchen. In that case, the starter may get icky - smell bad, get moldy, not bubble - and you have to try again. If you don't have natural yeast present, you need to add some yeast source such as the grapes mentioned in another review or even a packet of yeast.
This recipe is fixable! You need to add grapes, preferably from the farmer's market so they are pesticide free. They have wild yeast naturally living on their skins (so don't wash them before you throw them in). Keep them in those first 5 days, then you can toss the grapes & just maintain the starter indefinitely with additions of fresh flour and water, discarding excess volume as needed.
Sorry... this method didn´t work for me at all... After 2 days, it separated in the container, became orange, and started to smell awful (not like any sourdough starter, but more like a mix between a gym\'s bag and cat litter...). I scalded the container, and I tried twice with 2 different brands of unbleached flour, with the exact same result. I´m kind of sad, because I really wanted it to work :(