We have not seen the working of buried terra-cotta pots filled with water
as a watering system however we know of farmers having horticulture saplings
and shrubs watering their plants in the growing stage by half burying
regular glazed earthen pots habing a small hole on side wall of the pot to
allow water to seep into the soil. Pots are semi buried to enable the
farmer to add water occasionally.
One ingeniously developed drip irrigation practice uses earthen partially
glazed couplings of about 7 to 10 cm length placed at convenient dinterval
over the entire tube length to allow water to drip into the soil throuogh
coupling. Rubber or plastic water line is laid on the ground and not
buried. Both the practices are absplutely low cost. We feel that unglazed
earthen vessel or substance cannot hold to shape hence glazing cannot be
avouded. Best wishes.