For insulators you mostly specify real part and imaginary part of relative epsilon (e' and e"), or a single value for epsilon and a loss factor (tan(delta)).
As water contains contaminants you need to know the conductivity. Pure water has very low conductivity and therefore "relative" low loss (as only eps.r of about 80 dominates). Just traces of contaminants will increase the conductivity, hence the loss.
What is your frequency and are you simulating in pure, fresh or sea water?
If you want to measure conductivity of own samples, don't use your Ohm meter. You can't reliably measure conductivity with a 2 wire interface and DC (so you need an AC source).