any arduino board. the NodeMCU can be programmed as an Arduino, has more pins available for a starter unit than the D1 mini.
water is always dirty unless you distilled it yourself. with lab grade equipment and containers.
water has a low resistance. two wires in water with a multi-meter will offer about 5k ohms so water sensing is super-super easy.
arduino of any sort. and some wire. that is all you need.
output from a digital pin, input on an analog pin.
add a resistor if you like to protect the input.
and ESP8266 of any flavor will get you on the home wifi network, or you can log directly to your ESP8266 from a device on your home network.
you can use blynk to use your cell phone.
My suggestion is to buy any Arduino, an UNO is the standard that most people have, and get the nodemcu, V2 I believe is the one that just fits on a board so you can use dupont cables. V3 is too wide by 1 pin.
get a soldering iron, the cheap pencil type with heater control in the handle is fine for simple work.
search aliexpress and ebay for free shipping. that way you can buy stuff each week.
get a clear box to keep all the stuff you will buy and never use. some of us have a dozen such 'shoe box' size plastic boxes. some of us have spare rooms filled.
for a purchased water sensor, use ebay, look for soil moinsture sensor.
you should get one for $1, free shipping and it comes with some wires to connect.
you can just cut the ends off and either stick it so it touched the floor to detect for house hold leaks, or lay it on the floor for faster response.
as a start, before you buy anything, one tip is to use google and add the word arduino.
water sensor arduino
led arduino
coffee arduino
there will be thousands of hits, read a few and take notes of the other words used, then search them
flood arduino
water leak arduino
soil moisture arduino
soon, you will have a better understanding of what others have done.
matornei:
I want to be able to communicate via wifi because i'm not always home....
WiFi will only communicate inside your home, or close to it.
WiFi is an alternative to letting your Arduino communicate with another computer via ethernet or a serial link (or as a wireless means of letting the Arduino communicate with sensors).
If you want to communicate when you are not at home then you are going to have to set something up that uses the internet, or SMS or 3G.
