Green chunks in water??

[McHugh]

We live in the UK in a normal water area, not very hard or soft, and we’ve been having tiny bright green bits coming out of the taps for probably about a year now. They’re kind of chalky when you rub them between your fingers and disintegrate. The house is only 9 years old so seems odd for it to be a rotting pipe or something. It’s been clogging up our mixer taps behind the roses to the point where we’ve had to take them out and empty huge chunks of the stuff built up.
Does anyone know what this is or how to make it stop? Thanks