Is it a plantation or only few plants? If it is only few plants, you can use pots with drip system-pots with a hole at bottom side and fitted with cotton thread, and keep them around the coconut tree, at points where its leaf reaches-not slanting onto the stem.
If it is a plantation, contact us for a proper solution.
No ground water ? To dig a borewell ? There is certain mulching system to be used for conserving whatever water and maintain wetness of the land.
Please mail us for further details: E: greenlandfns@gmail.com