water level pump circuit
It looks like it should work, have you tried it out yet? You could simplify things a little by getting rid of the 4013, and making a cross-coupled latch out of the 4011 NAND gates. The latch has a disallowed state (both inputs at logic "0" for the NAND version, both at logic "1" for a similar latch made out of 4001 NOR gates ). Inverting the output of S1 bypasses the disallowed state, since S1 is never off when S2 is on. S1-Off/S2-Off resets the latch, S1-On/S2-On sets it, and there's no change during the S1-On/S2-Off state.
The latch can power up in either state when the water level is between S1 and S2. This could be an issue, since the pump could come on at power-up until S1 shuts off. Wiring S1 to the positive supply and using R2 as a pulldown would eliminate the inverter, though low-side switching is a better idea in case a short develops somewhere in the wiring.
You could use a schmitt-trigger NAND like the 4093, but there's no real need to, since the water level provides plenty of hysteresis.