Have you ever stayed out of town of noticed the quality of the water at a hotel or something can greatly affect how your hair looks and feels? I grew up on a peach farm in NJ and we had hard well water. My mom would get us huge 40lb bags of water softener pellets from the farm feed store we'd have to lug to the basement to keep our hair and skin nice. Now, personally, I have the type of hair you (dry/coarse/color-treated) don't have to wash for 4-5 days at a time. I can even put shine products on the ends and use heavy conditioner every time I wash. Because I do so much with hair coloring, I always have to use a sulfate-free shampoo (read:gentle) so I don't wash away my expensive dye job. I shower almost every day, but I've invested in high-end shower caps (avail at places like Marshalls) so I don't have to get my hair wet, washed and blown dry every day (Who has time for that?)
A couple years ago, my little sister Hollee moved into the nearby city of Philadelphia from our hometown. She said it was affecting her hair something horrible! Interestingly, when we were little, the style of slicking down your long side pieces into a deep part and plastering it severing to the head with gel was in style. You'd see all of the Philly girls wearing their hair like this. Well, now Hollee said she knew why: "That style caught on because of this awful city water!", she lamented. "There's nothing else can do with your hair! It's so greasy! I can't go to work like this!"
She began to look for answers. She came up with two really inventive holy grail product/tools for her greasy hair: 1) Aquasana shower head water filter and 2) Degrease shampoo. Now she won't use anything else!
An interesting and funny post-script to this story: I recently noticed my little sister washing her hair a couple months ago. I commented on the fact that she used very little shampoo in her hand. She replied, "Didn't Mommy force you to use only a dime-sized dollop of shampoo?!" Um, no my mom never taught me this and our mom swears Hollee is making this up! Now, Hollee uses a generous amount of shampoo these days - and as you can imagine! - her hair situation has improved that much more!