Use a mechanical clock to control "dripper irrigation" for your plants.

I attached the top of a bottle to the "key" for winding a clock,  hung the clock above my water container and string round the bottle top (as it unwinds with the clock running) drops a float that lets water out of the container.   The way of attaching the bottle isn't ideal but the clock key has a left hand thread so it's really hard to fit anything else to it.    I just drilled a hole in the bottle top,  then carefully heated up the clock "Key" with a ciggy lighter,  then pushed the key into the plastic to have a tight fit.  Currently the string drops at about half an inch per hour.   Wider "spool" for the string would mean faster string movement.  
Please give it a try,  thanks  Brian.   (You don't need to take the back off the clock,  I just didn't know how they worked so I just wanted to look).

That is a completely unique approach to the problem! It has a sort of Rube Goldberg / Heath Robinson feel to it. I like it!

If you are collecting BBs, this would surely be at home in the Oddball category.