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I have been wanting to add some water for increased biodiversity to our garden for a while but have been wary of open water due to small children concerns. 
I have recently had a thought due to some recycling opertunities coming along. 
I have a broken recycling box which is split down one corner and not useful as a recycling box any more. Also due to some recent house refurbishment and some hard landscaping I have some thick black plastic to use and a large quantity of rocks and stones of differing sizes. 
My thoughts are could I effectively make a submerged sump with the box and plastic, fill it with stones then fill with water? 
Could it be useful as a source of drinking water for birds, insects etc? Would it be useful at all and if so how?

We did something similar years ago. with a big tub that we sank in a corner bed on the patio. Put a wire grid over the top of the tub and covered it with pebbles. At that time, we could run the bubble fountain in the pump on mains electricity. Later used a solar pump which was less controllable.
Not sure that birds ever used it but the bubbling water sounds were very relaxing and it looked nice running over the pebbles.