Just started renting a flat and the shower is rubbish - what can we do?

It's not an electric shower, and the water tank is in the opposite end of the flat from the bathroom. Therefore no water pressure. It just dribbles out, it's useless. We are mortified at the thought of spending the next 6 months showering under this thing. Can we ask the landlord to have it replaced with an electric shower? It's all tiled in there - so it would be a pricey job I'm guessing. Would the landlord perhaps accept but ask us to pay? Where do we stand?