You followed the method carefully: no shampoo, no sulfates, no silicones, leave-in and gel on wet hair. Some weeks it works. Then your hair feels coated, heavy or flat, and the rules do not explain why. The method is not wrong for everyone. It was built around a general rule, and the chemistry of your hair and your water can be more specific than that rule.
What the method asks, and why it helped many people
The Curly Girl Method popularized avoiding harsh detergents, heat and some silicones. Many people report better definition and less breakage with it, and those experiences are the reason it spread. The useful question is which parts hold up when the variables change: water, drying time, climate and the products you use.
Curious how a routine is built from numbers like these? See how Rizzado works, step by step.
See how Rizzado worksHard water changes the rules
Hair can take up calcium and magnesium from water. Evans, Marsh and Wickett (2011) found that the condition of the hair mattered more than the water hardness. Uptake tracked how much the hair could bind (correlation of 0.98 to 0.99), more closely than the hardness of the water (0.59 to 0.72). Damaged hair took up more.
Luqman and colleagues washed hair from 70 men in hard water, deionized water and a control. Mean tensile strength was lower in the hard-water group, about 234 against 255 in the control. Other studies found no significant difference, so the evidence is mixed. Water is one variable among several, not a verdict on every curl.
Drying time is a variable too
Lee and colleagues (2011) compared drying methods on hair washed and dried repeatedly. They reported that air-dried hair showed damage to the cell membrane complex, which they linked to longer exposure to water. In their experiment, a dryer held about 15 cm away and kept moving caused less total damage. This is one small study, so treat it as a reason to test, not as a rule.
Buildup is a practical question, not a rule
Heavy oils and styling polymers can accumulate on hair. Whether a co-wash routine needs an occasional cleanse depends on what you apply and how often. We did not find a controlled trial that sets a frequency for every curl type, and this guide does not claim one.
Conditioners are formulated to condition, and cleansing surfactants are formulated to remove. Gavazzoni Dias (2015) reviews how shampoos, conditioners and other hair cosmetics are formulated, which is a useful reference for why the two behave differently.
What to test, in order
Start with your water. If your city has a published hardness figure, note it. Hard water is a reason to watch for residue, not a diagnosis.
Check your drying. If your curls look dull after air-drying in humid air, test a low-heat dryer held at a distance for two weeks before changing anything else. Clarify only when you can see the reason: if residue or heaviness appears, change one thing and compare the next three wash days. Keep what repeats. Rules are a starting point, and your results decide the rest.
CITY DATA
Compare a published local source
These pages keep the utility or public authority source next to the figure. They are a starting point for a question, not proof of what is happening to your hair.
Browse every city with a primary source