I have made a bird bath in my garden with a large plastic receptacle fashioned from a plant-pot saucer to hold the water. It has proved to be successful, with many birds using it each day, but I have found that algae build up very quickly on the surface covered by the water. The plastic receptacle was bought new from the shop and the water I put in it is good drinking water, so where do the algae come from? The birds bathe in it and drink the water without any obvious ill effects.
Calverley Redfearn, Carlisle, Western Australia