After ripping out your kitchen, examine the pipe-work that is left. It is likely that you will have to reroute it to make accommodation for the new design. Some parts of the existing plumbing work might have to be replaced altogether. Look out for any prominent leaks or weak spots and make replacements for these connections. It is rather easy to finish off the pipe-work before installing the kitchen units.

Before starting, go through the articles on earthing requirements and plumbing rules. It you have a doubt, make sure you get professional help. You may even refer to the articles available on plumbing systems installations.