When radiometric dating, would water affect the measured age of old rocks ?
Specifically would water affect Uranium-238 to Lead-206 dating of Zircon crystals?
Would it affect the lead since it’s slightly soluble in water?
No, not really. In simple terms, to be soluble in water, Pb must be in contact with it. But most of Pb is stored within the Zircon lattice, where water cannot diffuse through. For example, many zircons in metamorphic and magmatic-hydrothermal settings experience supercritical fluids, but preserve their U/Pb ratios (e.g. inherited cores in metasedimentary zircons). However, metamorphic events themselves can lead to Pb loss, which you can correct with a Tera-Wasserburg approach.