When you do laundry without using detergent the clothes will still get somewhat clean with just the water.
But when the clothes or laundry is not washed with detergent the clothes may still have some dirt and grime on them and they may still smell especially if the laundry is really dirty.
Washing out clothes and laundry without detergent and with just water can be done if you have no detergent or you can use some vinegar in the washing machine to clean your laundry and clothes without detergent.
But it's best to use laundry detergent to clean your laundry and clothes.
You could also use some dish detergent to clean clothes or use shampoo to clean laundry and clothes with when you run out of laundry detergent.
However washing your clothes or laundry with just water is better than not washing them at all.