There are series of stream pools in the rockery. Water circulates from the ponds up to the top pool and then back to the ponds and also comes from the various buildings when it rains.
The top pool is a favoured spot for frogspawn.. It is a safe haven for them with no fishy predators. Also, the rockery provides an ideal habitat for the baby frogs when they leave the water after metamorphosing from tadpoles. The flow of water (and leakage from frost-damaged concrete) creates mossy areas loved by the bees for collecting water for the hive.