There can be several reason's why you have low water pressure. If it's only in the bathroom or the shower fixture? If it's the shower fixture then there might be a washer in there to save water and thus low pressure too. Is there low pressure thru out the house?Then it could be a problem with the water main and then I would call the water company to ask them what there problem is.This can go on and on.....Good luck and post back.