This video explains how you can extend your existing mains water supply from your house and install the mains water pipe for you garage conversion.
Keep your eyes peel for more out building video on my channel.
Here are some of the products I used in in the video if you're looking to make the same kind of set up:

MDPE Mains Pipe 25mm X 50M/25M : http://amzn.to/2qXcREz

Philmac UTC (Universal Transition Coupling) 25mm X 2117mm: http://www.plumbcenter.co.uk/product/...

MDPE Equal Tee Junction 25mm: http://amzn.to/2qSp2aI

Stop Cock 25mm to 22mm: http://amzn.to/2rsh8Du

Drain Off Cock 22mm: http://amzn.to/2qSrcaq

Thank you so much for look.
Best regards, Matt