Safest way to use water sensor?

Projects General Guidance
1

I'm working on building an automatic water fill system for a pool using the Arduino Uno to activate a relay that opens a water solenoid valve. There will be a sensor at the pool that closes when the water level drops below it . I'm sure i can figure out the circuitry but my real concern is about safety since water & electricity can be dangerous. I work with electricity so i know how to isolate different circuits & I want to be cautious about what can happen if any the Aruino IO's are going through the water. Since I'm only using the sensor to tell the Arduino what to do there shouldn't be much current flowing through it but I'd like to get some advice from anyone who is familiar with the capabilities of the Arduino's current flow.
1 - Do i need a specific type sensor or resistor or just anything that will close & open depending on the water level?
2 -Isn't any commercial electronic water flow system still going to have to have some small amount of voltage or current going through it too?

Here's a link to the system that is on the pool now that has to be replaced about every two years & that's why i'm trying to make one that will do the same thing.
http://www.poolsupplyworld.com/Jandy-K1100CKA-Levolor-110-110220V-with-Sensor-50-and-1in-Valve-Water-Leveling-System/K1100CKA.htm

2

The voltage used in water level sensing is very small and is safe.

I could not load the link supplied.

Do a search in the box at the t of this page for water level sensing. It is a common topic.

Weedpharma

3

almost no data available on the sensor part.

this is one part number from the parts list
http://www.amazon.com/Zodiac-S3040A30-Contact-Replacement-Leveling/dp/images/B008E6RHSA

if you replace this, what do you replace ? it seems like there is little to fail.

for a high water level sensor, you need two sets of sensors.
one for the low water mark, then one for the high water mark.
or you can measure water level as an analog, either from pressure or distance, or direct water level.

I cannot think of any sensosr for that that would be un-safe.
all use too little power and none require actual contact with electronical bits and water.
except for the two electrode type.

I would wager that whatever sensor this device uses, would offer output that the Arduino can use.

can you post engineering data, link, photos, whatever, about the existing water sensor ?
the one I posted says it is discontinued.

but, on first guess, it is a capacitance, continuous water level sensor, two aluminum or stainless tubes. completely sealed with insulation so they never get wet. this means no electrical contact with the water.
the water level changes the capacitance, and you can use a capacitance sensing library with any arduino.

the reason I would wager that it is no a resistance probe is because the chemicals in the water could greatly effect resistance and throw readings off very easily. some spas use salt, some ozone. you would have to calibrate the device for the chemicals used. PITA.

4

I can't find any data on the sensor that is used but couldn't I use anything that will just stay NC or NO when it is above water & reverse the points when it is below water depending on how I set it up with the Arduino?

5

I was just explaining how to build a water level sensor that wouldn't produce any metal ions for a grow system. So, I'm checking out Pad2Pad prices because, if you have two conductive planes, you have a capacitor. The circuit board material can be produced with a layer between the sheets of insulating laminate. Two parallel planes make an air gap capacitor, where air has a dielectric value of 1, and water is 80. So, if all you do is measure the capacitance of the two plates, the highest capacitance is when the tank is full, and the lowest, when it's empty, and the plates only need be as long as the tank is deep. No chance of arcing. The value of capacitance when the tank is full should be about 80 times higher than if it were air between the two insulated plates.