The path to the water is treacherous. The snow has covered the ice making it slippery underfoot. It is 7.45 am and dark, but my friend Vicky and I have head torches and the moon is bright. Our walk – prior to lockdown 2021 – is through the woods and down the path to the edge of Threipmuir reservoir in the Pentland hills, just south of Edinburgh. It is impossible to tell where the water starts as everything is covered in a thick layer of snow..