Would (3) float switches with runs of 5, 10, and 70ft work with a single Arduino?
Are the floats a better choice then the diagram above?
(2) floats will be in sump pits and I am not worried about a wire breaking. Is there any worry of a normally closed switch seizing itself from not being activated for months or years?
For the EMI it may be a good idea to add a small bypass capacitor (10-100 nF ceramic), and possibly a stronger external pull-up resistor instead of using the internal one (start with 4k7). Capacitors may also be a good measure for the other two, with shorter wires.