Because there are some concerned people, here some explnanations:
There are three forms of water:
H2O, the normal stuff
D2O, heavy water, not radioactive
T2O, tritiated water, radioactive
Here a link dealing with heavy water:
Heavy water is also widely used in science, because it is 10% heavier as
normal water and can be detected, for example, with a mass-spectrometer.
What we do:
We want to produce plants, which contain different types of stable (not
radioactive) isotopes, such as 13C, 15N or 2H (Deuterium). Therefore we let
the plants grow in a gastight growth chamber, which controls the
temperature, humidity, light and the concentrations of CO2 and O2 in the
atmosphere. It measures online the photosynthesis and respiration (if
someone is interested: www.gms-biobox.de).
These plants are fed to certain bacteria. The bacteria produce certain
proteins, which play a possible role in medicine.
Some scientists want to know the 3-D-structure of this proteins. Therefore
they use a technique called NMR. And this is just working, if there are
different isotopes of an atom in a protein.
I hope this short explanation is helpful,