According to this...

According to this site,http://www.aer.gov.au/content/item.phtml?itemId=730187&nodeId=d0b7cae484b3e261c18d06c74c9e4290&fn=EnergyAustralia%20-%20distribution%20loss%20factor%20calculation%20methodology%202009-10.pdf
P.5,
overall distribution losses are around 5%. This does not surprise me. Very long transmission lines would make this worse.

Now if you were to use pump storage you lose 5% when "buying" power to pump the water uphill, another 5% when "selling" the power plus pumping and generating inefficiencies. Maybe 50% loss overall?