Electronic – water level sensing electronically

I am working on an electronic water sensing mechanism.

In an underground water tank I need to sense various levels of water as the water level is consumed and refilled. Later I want to control the sump motor with logic when various conditions are met.

Docusing on just electronic sensing mechanism there are many choices available

• bias a transistor with the help of water as conductor
• use Logic gate inputs to become HIGH/LOW when water touches probes.
  Several choices for gates, any gate can be used in general, even a NOT gate can do.
• Ultrasonic depth sensing.
• LDR based
• various other.

I am working with logic gates at the moment but will transfer it to micro controller later when I am satisfied with 'water sensing'.

The problem with many techniques above are, their reliability changes with many environmental effects. water vapours, hydration, corrosion, electrolysis, temperature and many similar factors change parameters which can affect changes in sensing.

Currently I am working with NAND CD4093. It has built in Schmitt trigger so it can shape inputs.

I prefer to give oscillated inputs to this logic gate, so at least electrolysis can be prevented. probes will be usually dipped in water.

To perform oscillation in sensing probe I can use transistors (AC biased), 555, opamp.

Q.1 Which one would be better option for oscillating in this scenario?

Q.2 How can I simulate the properties of tap water in reservoir e.g. water conductance and other electrical properties in NI multisim?
currently I GND the inputs with a switch to give the effect of water touching the probes in NI MultisIM. How I can model the real water properties effecting my probes

Q.3 any other idea to achieve the task?

I want 8 points of level detection, each point is one foot higher than previous one.

From full to empty, the difference is approx is approx 10 feet. This is an underground tank of concrete.

I want it reliable and long lasting, free from errors and safe from enviromental changes. a one time install solution, no corrosion at probes, no electrolysis, no
reading errors due to temp changes, hydration, vaporization, …

Tank bottom is approx 10 feet from top.

Level readings at the moment will only light up LED's but at the next phase they will be the inputs to a micro controller based logic algorithm implementation where two pumps will be in service in parallel but one at a time, next time next up, will take turns. several conditions will be checked to turn the right pump, or to just give warning beeps. and more … but this all will come in next phase, later.

• • • Updated – – –

I understand all three oscillators I mentioned, AC biased transistors, 555 clock generator, OP AMP generating square waves.

I want an oscillator which will oscillate in +ve and -ve polarities, this scheme can avoid electrolysis.

I think OP AMP will do that better.

Now how to make the reading from probe non-oscillating so that it can be fed to a logic gate, otherwise logic gate output will also oscillate.

Should i use de-bouncing before giving input to logic gates

Are there any stray capacitive/inductive or other parameters in tap-water other than the conductance (or resistance) that should be taken care considering digital inputs?

I am trying to avoid any commercial sensors. I prefer building my own.