Aland, what type of building construction is this?.
And also, what type of utilisation?
What type of water mains do you have?, copper?, plastic?.
Also is there a common area where you can place an Earthing Enclosure, where you can run 16-25mm2 earthing conductors in conduit and Bond the whole lot?.
Even if you have to drive stakes at each end of your ECC's, it would have the effect of lowering your Earthing Resistance.
Let's face it, these days if you're not young, you're old - Red Green