I'm currently considering an unlimited water generator based on the water freezing/melting processes in the game.
The generator is supposed to work as follows.
1. Starting condition. Outside ice block is frozen and rests on a stone floor (constructed or natural). Magma-fall below is not working.
__###
=>
###_####
## <= ##
## => ##
##7#####
########
2. Magmafall is activated and in 2 steps it puts a 7/7 block of magma below the ice block.
__###
=>
###_####
##7<= ##
## => ##
## #####
########
3. Ice melts (this happens nearly instantly as far as I can tell).
__###
=>
##7_####
##7<= ##
## => ##
## #####
########
4. Now the 7/7 block of water spreads into the adjacent inside underground empty tile...
__###
=>
##43####
##7<= ##
## => ##
## #####
########
5. Where it is immediately pumped into an underground waterduct.
__###
=>3
##4 ####
##7<= ##
## => ##
## #####
########
6. Finally the gravity takes over, the magma block falls and the 4/7 (or 2/7) water on the open tile freezes back to a natural ice block.
__###
=>3
###_####
## <= ##
##7=> ##
## #####
########
The cycle repeats over and over.
Since gravity in DF affects both magma and water, and due to it's semi-random nature, about 50% of the cycles will be "empty", because magma block will drop and the water re-freeze before it has a chance to spread to the adjacent tile. Otherwise, the design should be reliable enough.
Comments/criticism/suggestions?