Health · Everyday health
How Water Helps Prevent Kidney Stones
Quick answer
Kidney stones form when chemicals in urine become concentrated enough to crystallise, so drinking enough fluid to keep urine dilute is the single most useful prevention step. About 1 in 10 people get a stone at some point, and about half of them get another. Cutting salt, keeping calcium in your diet and limiting animal protein also help.
What is a kidney stone?
The National Kidney Foundation describes a kidney stone as a hard object made from chemicals in the urine. When those chemicals — calcium, oxalate, uric acid, cystine and phosphate — become concentrated, they can crystallise and form a stone. That single sentence explains why fluid matters so much: dilute urine gives chemicals less chance to clump together.
How common are kidney stones?
About 1 in 10 people will get a kidney stone at some point in life. The National Kidney Foundation reports rates of about 11 per 100 for men and 9 per 100 for women. And once you have had one, roughly half of people get another — which is why prevention is worth real effort after a first stone.
What kinds of stones are there?
- Calcium stones are the most common, either calcium oxalate or calcium phosphate.
- Uric acid stones are often linked to gout or eating a lot of animal protein.
- Struvite stones are rarer and usually follow a urinary tract infection.
- Cystine stones are rare and caused by an inherited condition called cystinuria.
How much should you drink?
There are two ways the official sources express this. The National Kidney Foundation frames it by output: drink enough fluid to produce about 2.5 litres (85 fluid ounces) of urine a day. NIDDK frames it by intake: unless you have kidney failure, many health professionals recommend six to eight 8-ounce glasses a day, which comes to roughly 1.4 to 1.9 litres.
The output measure is the more useful one, because it accounts for how much you lose through sweat. If you are working outdoors in hot weather, you will need to drink more to produce the same amount of urine than someone sitting in an air-conditioned room. Important exception: if you have kidney failure or have been told to limit fluids, follow your doctor's instructions rather than these general figures.
What else lowers the risk?
NIDDK's dietary advice covers several points:
- Salt: adults should have less than 2,300 mg of sodium a day. For scale, one teaspoon of table salt contains about 2,325 mg — so a single teaspoon is the whole day's allowance.
- Calcium: despite the name "calcium stones", getting enough calcium actually helps prevent them. Do not cut calcium out on your own.
- Oxalate: people prone to calcium oxalate stones may be advised to reduce high-oxalate foods such as nuts and nut products, peanuts, rhubarb, spinach and wheat bran.
- Animal protein: limit beef, chicken, pork, organ meats, eggs, fish, shellfish and dairy, and get more protein from legumes, soy products and seeds.
- Fruit and vegetables: eat more of them. The DASH eating pattern is associated with lower stone risk.
- Weight: keeping a healthy weight matters, particularly for uric acid stones.
The National Kidney Foundation also advises limiting added sugar and avoiding nutritional and herbal supplements when you are prone to stones.
What does a kidney stone feel like?
Symptoms depend on the size of the stone, and the National Kidney Foundation lists:
- Severe pain in the lower back, on one side
- A persistent, vague ache in the stomach that does not go away
- Blood in the urine
- Nausea or vomiting
- Fever and chills
- Cloudy or foul-smelling urine
Who is at higher risk?
Alongside a previous stone, the National Kidney Foundation lists diabetes, inflammatory bowel disease, polycystic kidney disease, gout and repeated urinary tract infections as conditions that raise your chances.
When to see a doctor
See a doctor if you have severe pain in your back or side, blood in your urine, or symptoms that keep coming back. If you have had a stone before, ask your doctor what type it was, because prevention advice differs by stone type and a dietitian can tailor it.
Get emergency care straight away if you have:
- Severe pain you cannot control, especially with vomiting
- Fever and chills along with the pain — this can mean an infected, blocked kidney
- Visible blood in your urine
- Being unable to pass urine at all
- Feeling faint or very unwell with the pain
In these situations, call Rescue 1122 where available, or go to the nearest hospital emergency department.
Frequently asked questions
How much water prevents kidney stones?
The National Kidney Foundation suggests drinking enough to produce about 2.5 litres (85 fluid ounces) of urine a day. NIDDK puts it as six to eight 8-ounce glasses daily, unless you have kidney failure.
Should I stop eating calcium-rich foods if I get stones?
No. NIDDK explains that getting enough calcium actually helps prevent calcium stones. Talk to your doctor or a dietitian before cutting calcium out.
How much salt is too much?
NIDDK advises adults to have less than 2,300 mg of sodium a day, and notes that a single teaspoon of table salt contains about 2,325 mg.
If I had a kidney stone once, will I get another?
Roughly half of people who have had a stone get another one, according to the National Kidney Foundation, which is why prevention is worth taking seriously after the first.
In an emergency call Rescue 1122 where the service is available, or go to the nearest hospital emergency department.
Sources
- Kidney Stones — National Kidney Foundation
- Eating, Diet, & Nutrition for Kidney Stones — NIDDK (NIH)