Dad’s short answer: Four causes, in the order to check them: too much water, a dirty roller, too much or the wrong solution, or a machine whose suction can't keep up. Three of those are free to fix.

Work them in order

Water level first. Most streaking I see is a machine set to high water on a floor that doesn't need it. Turn it down a notch and run the same stretch again. On smooth, glossy floors especially, less water gives a better result.

The roller second. A roller that's carrying grime from previous runs smears rather than cleans, and it will look exactly like a streaking problem. Pull it out, look at it, and if it isn't genuinely clean, that's your answer — and it means your wash or dry cycle isn't doing its job.

Solution third. More cleaning solution does not equal cleaner floors. Excess detergent leaves a residue film that dries streaky and then attracts dirt, so the floor gets worse over time. Use the dose on the bottle, not a generous glug.

The machine last. If water, roller and solution are all right and it still streaks, the suction isn't lifting enough water off the floor. That's a hardware limit and it's most common on budget units.

The squeegee difference

On shiny floors — marble, polished tile, high-gloss LVP — a machine with a rubber squeegee at the front makes a visible difference. It wipes the last film off behind the roller before it can dry into a streak. If your floors are glossy and streaking is your main complaint, that's the feature to shop for next time.

Dad’s Take: Nine times out of ten it's too much water or a roller that isn't as clean as you think it is.