Thank you for the information,
There can be a number of causes of cramps of the legs at night which may occur during the day too.
Dehydration, deficiency of calcium, magnesium, potassium, sodium-electrolytes, vitamins , muscle fatigue etc. can cause cramps.
As you are taking diuretic, dehydration, electrolyte loss/ imbalance is possible.
There can be other conditions too.
Peripheral artery disease causing circulation abnormalities also can cause muscle spasm.
Systemic diseases like diabetes , low thyroid, Parkinson's disease, liver & kidney disease & others can be associated with it.
Sometimes no cause can be apparent too.
If it continues to recur, I feel you should have an examination by doctor.
You may try some home measures-
Take plenty of fluid, fruits, vegetables etc.
Electrolyte solution like gatorade can be tried.
Avoid coffee, alcohol, tobacco
Stretching, warm bath can be taken.
Vitamin and minerals, calcium supplements can be taken.
I hope this information helps.
I will be happy to assist, if you need any clarification.
Please feel free for any follow up query.