Pure water has no colour. Water can contain minute suspended particles that affect the colour. Water draining from peaty ground may have a slightly yellow hew. Water containing a fine suspension of clay particles has a milky or opal blue colour.
Water absorbs and selectively filters white light which is made up of all the colours in the rainbow. Long wave Red Light is absorbed much more than short wave Blue
The further light travels through water, the more blue it becomes. Travel down into the deepest ocean and eventually all light will be absorbed, leaving total blackness.
In the 1960’s the Torwood Blue Water Pool deserved its name as the light coloured brickwork reflected a lot of light back up to the viewer’s eye. The Pool is 5 metres deep so the light travels 10 metres through the crystal clear water and comes back with a genuine blue colour — not milky but crystal clear like a blue diamond.
Today the bottom of the Pool (and a fair way up the sides) is covered in very dark silt and weed. This dark surface absorbs ALL light indiscriminately and only a small amount of light makes it back to the surface.
The dark green colour has a lot to do with reflection of the green trees growing almost over the pool. The occasional stunning blue is a reflection of the blue sky.
If we cleaned out the Pool and painted the brickwork white, we would have the most stunning of crystal clear Blue Water Pools.