Thats about normal in the UK
According to my water company for the year 2006, the average level in my tap water was 29.8 mg/l
It's very annoying to have this level straight out of the tap, and for me its the biggest arguement for Reverse Osmosis (RO) water
As you may already know, the legal limit is 50mg/l
And when i looked at other water authorities, i think i must have checked at least 30 different ones all over the UK, none of them had an average reading of LESS than 18 mg/l hence why i say your 23 mg/l is (unfortunately) NORMAL levels