Hard water coupled with powdered detergent can prove be a nuisance, especially for your dark colored clothes where they leave stains and streaks. This is because powdered detergents don’t fully dissolve in hard water and can cause patches which might not be visible on light or white clothes.
To prevent such streaks, make sure to let the detergent diffuse through water in the top load washing machine’s wash before immersing the laundry in it.
For a front-load washer, it is advisable to replace your powdered detergent with liquid detergent. If not, then preferably dissolve the powdered detergent in water before pouring it in the machine.
Moreover, to get rid of hard water stains, the vinegar solution method like liquid detergents as mentioned above can be applied in this situation too.