If the abs lamp comes on while driveing its normally a abs wheel sensor at fault.

if it comes on after going through a large puddle it could be the sensor cant do its job
as its to dirty ect. as it drys out and you stop and then start the engine again the abs
ecu does its checks and all is fine.
take it to your local garage who should be able to do a simple check to find out
if the abs ecu has stored a code.
hope this helps

Dave