Water-filled waveguide from PCB laminate, Cu layer on the outside

Can I use a 1 m long waveguide at 200 MHz, if it is filled with distilled water (then the wavelength will be about 18 cm), and made from copper-clad PCB laminate with the Cu layer on the outside? Won't I have problems with total internal reflection at the water/PCB dielectric interface?

A dielectric layer d << λ can't cause total reflection. But surely changes the E-field distribution.

Did you estimate the losses due to the water RF absorption at 200 MHz? I fear, it's huge (possibly in a several 10 db/m order of magnitude).

Dielectric loss in water is 0.64 dB/m, so it is acceptable for me.
How should I estimate the E-field distribution in the presence of, say, 2mm layer of PCB dielectric?