Suffering from water hammer I'm thinking of installing a water hammer arrestor ? I have 2 stop cocks in my house for some unknown reason. The stop cock in my kitchen only supplies cold water to kitchen sink and bathroom toilet sink and electric shower . The other stop cock comes out the ground in a rear utility room. After the stop cock it branches off one goes to my boiler which then feeds hot water to taps the other branch feeds the utility rooms toilet and sink and then to the washing machine . The stop cock in the utility room is the one that is causing the water hammer so if I turn off taps use washing machine it makes a loudish grumble but not at the source always at the end of the line which is in the bathroom somewhere .. Where would be the best place to fit a water arrester to see if it solves the problem .