Anyone who has passed a kidney stone has been told to drink more water. It is sound advice and it is also unhelpfully vague. More than what? For how long? Does it need to be water specifically?
Stone disease recurs in roughly half of people within several years, so these questions are worth answering properly.
The target is urine output, not glasses of water
This is the part that usually gets lost. The goal is producing at least two to two and a half litres of urine a day. How much you need to drink to achieve that depends on how much you lose elsewhere.
In Mumbai, that difference is considerable. Someone working outdoors or commuting in humidity through May loses a great deal through sweat, and none of it reaches the kidneys. The same intake that works comfortably in January may fall well short in the pre-monsoon weeks.
There is a simple daily check that removes the guesswork. Look at your urine. Pale straw or near colourless means you are where you want to be. Deep yellow means you are behind. It is crude, it is free, and it tracks the thing that actually matters.
Why dilution works
A stone forms when the salts dissolved in urine become concentrated enough to crystallise and stick together. More water means the same quantity of salt is spread through more fluid, so it stays dissolved and passes out harmlessly.
The timing matters as much as the total. Drinking two litres in the evening does not protect the eight hours you spent concentrated during the day, and it guarantees a broken night. Spreading intake across waking hours keeps urine dilute continuously, which is the point.
Overnight is the longest gap without fluid, which is why a glass of water before bed is often suggested for repeat stone formers.
What to drink
Water is the simplest answer and there is no need to overcomplicate it.
Beyond that, a few things are genuinely useful. Citrus, particularly lemon and lime, adds citrate to the urine, and citrate binds calcium and interferes with crystals forming. Fresh lime juice in water is a reasonable habit for people who form calcium stones.
Regular tea and coffee in normal amounts do not need to be avoided. Very high intakes of cola, sugary drinks and iced tea are less helpful.
The three changes beyond fluid
Reduce salt. This one surprises people because it seems unrelated. High salt intake makes the kidneys excrete more calcium into the urine, which raises the risk directly. Most of the salt in an Indian diet comes from pickles, papads, packaged snacks, processed foods and restaurant meals rather than from the salt shaker.
Do not cut out calcium. This is the most persistent myth in stone disease, and it makes things worse. Dietary calcium binds oxalate in the gut so that it leaves in the stool rather than reaching the urine. Cutting calcium increases oxalate absorption and increases stone risk. Normal dietary calcium in food is protective. Calcium supplements taken between meals are a separate matter and worth discussing.
Watch animal protein. Large amounts of red meat, poultry and fish raise uric acid and lower urinary citrate, both of which favour stone formation. Moderation is enough. Elimination is not required.
When prevention needs to be specific
General measures cover most people. Some situations call for a proper metabolic assessment, meaning stone analysis alongside blood and 24 hour urine testing:
- More than one stone episode
- A first stone before the age of about thirty
- A family history of stones
- A single functioning kidney
- Stones alongside gout, inflammatory bowel disease or previous bowel surgery
The point of that testing is to stop guessing. Different stone types have different drivers, and prevention aimed at the actual cause works far better than general advice applied hopefully.
The short version
Drink enough to keep your urine pale, spread it through the day, go easy on salt, keep calcium in your diet, and get a proper metabolic assessment if you are forming stones repeatedly. It is unglamorous, and it prevents a great deal of pain.