I recently leased a house and the water pressure is not all that great... when I looked in the basement and under the house the water lines or pipes (some kind of flex white PVC)are on the ground in some areas... the way one pipe is joined to the next (some appear to have been to long) so instead of shorting the pipe before joining it to the next pipe it was joined to the next pipe, the pipes go up, down and in some areas they are running along the ground and in other areas they appear to loop before they continue to the next joint. Can this be the reason for the lack of water pressure ?
I am considering purchasing the house and would like to know if the property should be re-plumbed before the I move forward?

Yes, the longer pipe you have the more pressure you are losing. Also, the more elbows you have installed on your plumbing system - the more pressure you will loose.

Here in California , we have our homes inspected prior to sale of house through escrow. Seller pays for the inspection. The inspectors are not necessarily the most knowledgeable tradesmen ( it is not regulated business ) but they point out the obvious stuff. The Seller may be required to either fix it - or as it is a case in most cases, they'll give you a generous credit for the repair and you hire your own plumber.

Call in a home inspector before you sign anything. Have him list the faults and any code violations that he may find. You now have ammunition to take to the table when you negotiate for a lower purchase price. Good luck and thanks for rating my reply. Tom