Yes, I washed my mala a couple of times, after years of daily usage I think it's not excessive. I just wash it under luke warm water with the same soap I use to wash my hands. The beads of a lotus seed mala will swell a bit (is that the right word?), better not let it get wet if the string sits very tight.
Now you can say that I've grown bitter but of this you may be sure
The rich have got their channels in the bedrooms of the poor
And there's a mighty judgement coming, but I may be wrong
You see, you hear these funny voices
In the Tower of Song