BMW windscreen washer on the blink?

The nearside windscreen washer works, but not the offside. Every now and then, a dashboard light comes on, indicating the windscreen wiper fault, but both wipers operate. Then the light goes out, but might come on again sometime after I've started on the next journey. I assume it's electrical, but is there a separate fuse for each washer? Seems unlikely. The jets rae clean, so no blockage there, and the reservoir's full.