A high calcium and magnesium content will tell you that mineral build up will indeed be an issue for you. This means that you may have to clean your mister nozzles more often.
Free chlorine content and/or chloramine content is good to know. You do have a low content, but be aware that certain times of the year, especially spring, they may do shock treatments (short term higher doses) to combat algae growth.
Another category to look out for is heavy metals. These can accumulate within the body and be slow to flush or never flush out (like lead, which binds to the bones). Heavy metals to look for include lead, copper, mercury, arsenic, and cadmium. Also, look for fluoride - some places fluoridate the water. The US EPA has set limits on allowable contaminate content for hundreds of items (not sure what the UK limits would be, but they are probably even stricter):
http://water.epa.gov/drink/contaminants/basicinformation/index.cfm#llink
In my opinion, it's not any one thing that by itself is necessarily a concern (unless you have levels outside EPA regulations). It's the combination of things. If you are in the upper range for several contaminants plus high mineral content plus fluoride plus high chlorine, for example, it may be time to consider distilled water or looking into an RO system. I don't know that anyone has done any definitive studies on water quality and chameleon health, and I know that many (if not most) keepers do use tap water. It's a judgement call that you will have to make.
If you want to post a link to the water quality report, we might be able to help you decipher the info.
