There is a reciprocal healthcare agreement in place between the UK and Russia, and as such every traveller to the country is guaranteed health care provision in state owned hospitals however, you should still ensure that you have adequate travel insurance that will provide you with sufficient cover to meet expensive medical bills and/or repatriation expenses should they need to return to the UK for treatment.
Hospitals throughout the country vary in quality from place to place, although on the whole health care provision is good in Russia.
Tap water is not always safe to drink in Russia, and you should also avoid having ice in any drinks. Drink bottled water wherever possible.