Pulled the car out of the garage this morning and the coolant light came on. It was fairly well below the 'Min' level on the header tank so I topped it up. After a short 7-8 mile journey, returned home and noticed slight steaming above the bonnet on the offside. The coolant level had dropped slightly so I pulled the lower plastic grille off, and sure enough the auxiliary rad matrix was wet and there was some coolant on the deflector lip on the undertray.
Just a few question guys:
1. I assume it's a bumper/grille off jobbie, but is it a fairly straightforward job to replace it?
2. Is it worth replacing both rads at the same time? As far as I know, they're both original.
3. I topped up with tap water, then read Murph's 'coolant' thread and realised I should have used the proper stuff

Should I drain the entire system down and refill with the proper coolant?
As always, any advice would be appreciated
3.
Misano Red B7 RS4 Avant. 20" Rotors. KW adjustable spring kit. 8 & 10mm H&R spacers. MRC Stage 2 remap. Pre-cat delete & x-pipe.