Dopamine is not a drug or some magical case ,It is a neurotransmitter (Neurotransmitters are endogenous chemicals that enable neurotransmission. It is a type of chemical messenger which transmits signals across a chemical synapse).
Its main source of origin is Substantia nigra; ventral tegmental area;
FIG.1 the one shown in red .
so It is an amine synthesized by removing a carboxyl group from a molecule of its precursor chemical L-DOPA, which is synthesized in the brain and kidneys.
dopamine signals the perceived motivational prominence (i.e., the desirability or aversiveness) of an outcome, which in turn propels the organism's behavior toward or away from achieving that outcome.so basically this neuron when activated produce reward giving system which means that if dopamine increased much which is not require it is harmful and also if it is not in certain level then also it it harmful ,
In blood vessels, it inhibits norepinephrine release and acts as a vasodilator (at normal concentrations); in the kidneys, it increases sodium excretion and urine output; in the pancreas, it reduces insulin production; in the digestive system, it reduces gastrointestinal motility and protects intestinal mucosalymphocytes. With the exception of the blood vessels, dopamine in each of these peripheral systems is synthesized locally and exerts its effects near the cells that release it.
so in the structure it is seen that there are two HO ions associated with benzene ring which is attached to one amine group so if this structure occurs repeatedly the more HO ions will be needed to complete the dopamine structure or to increase dopamine ,
HO ions are easily available in water ,by calculating HO ions in 1 mole of water molecule it is found that there are 6.023*10^23 number of constituent particle .
molecular structure of water
for this case 1/22.4* 750 ml/m
which is 3.5 liter
so drinking approx 3 to 3.5 liter water per day can activate dopamine neurotransmitter.
also activate reward giving system of basal ganglia .