Cloth diapering ease is often dependent on the quality of water used to launder diapers. Most of us in the United States have hard water and it shows up as stains on our shower curtains and build-up on our cloth diapers. Selecting a detergent that performs well in hard water is key to a happy cloth diapering experience. Don't assume you have hard water just because a majority of people do. Some areas of the country have naturally soft water, which means you'll need less detergent to get the same amount of cleaning power. If you have a water softener installed you're in luck: you have soft water.
If you don't know what type of water you have (hard or soft), it's worth finding out. This is a simple task. The first, and probably easiest way, is to purchase a test strip. You can find these at your local pet store (aquarium section- look for a variety that will read water softness), or purchase one online. Rockin' Green makes their own test strips. Another way to figure out what type of water you have is to call your utilities company and ask. If you suspect that you have very hard water, you might be interested in contacting a company that sells water softeners and having them come out to test your water and discuss water softening options. We tested our water using a test strip, and had good success with that option.
The most important thing with using a test strip is to read the directions for use. Typically, you dip the test strip into a cup of tap water for 1 second and read the results after 30 seconds. To interpret the results, you will compare the color of your test strip to a range of colors representing different levels of water hardness. Our water is naturally soft, and we test in the soft range.
The test strips from the aquarium store give me additional information about our water. I can see how high the chlorine level is and find out if our water is slightly acidic or slightly basic. Our water is slightly acidic. We are at a pH of 6 (7 is neutral: not acidic or basic). Therefore, I would not want to add vinegar to my already acidic water. Adding 1/3 cup baking soda to a washer full of water spikes the pH to over 8. Now my water is too basic. This is why adding baking soda or vinegar to cloth diaper laundry can create problems. pH is a complicated thing and it would take me a lot of experimenting and water testing before I optimized the water in my washing machine to a pH of 7. Optimizing the water pH to 7 will not help my laundry get cleaner, so it's not worth my time. The amount of laundry detergent added during the wash cycle is more important.