For all types of stones increasing water and fluid consumption is a primary component of treatment to increase urine volume.  By increasing the volume of urine, it becomes more dilute.  Salt crystals (i.e. calcium oxalate, calcium phosphate, uric acid and cystine) are less likely to form/precipitate in a large volume, dilute urine.  It's the same concept as pooring table salt into water.  The more water, the more salt it can hold without salt crystals forming.  

Other dietary interventions are directed towards the type of kidney stone that forms and also possible underlying medical conditions.  The dietary interventions for specific types of stones or associated diseases are discussed below.

Calcium Oxalate associated with hypercalciuria:  People with  hypercalciura excrete too much calcium into the urine.  It is a genetic disorder that runs in families and is very common amongst people who form stones.  After other causes of high urinary calcium are excluded (including high salt diet, hyperparathyroidism, certain cancers, and sarcoidosis) dietary treatment includes increasing water/fluid intake and a low protein diet.  Protein in the diet increases calcium loss in the urine.  Dietary changes usually do not include restricting dairy or other calcium containing products.  In fact, people with this disorder lose significant amounts of calcium from their bones.  If calcium intake is limited, additional losses in bone density can occur.  In addition, calcium in the diet at mealtimes binds to oxalates contained in the food.  The resulting calcium oxalate complexes are incapable of being absorbed in the gut and are passed out of the stool.  Therefore, diets containing calcium (i.e. dairy) are likely to decrease urinary oxalate levels.  

Calcium Oxalate with hyperoxaluria:   Hyperoxaluria refers to high levels of oxalate in the urine.  Oxalate and calcium combine in the urine to form calcium oxalte crystals and stones.  Oxalates are originally absorbed from food.  Some people have genetic disorders with extremely high levels of oxalate in the urine.  Most, however, have less severely elevated levels associated with high oxalate containing diets.  These people have Dietary Hyperoxaluria.  In both disorders, limiting the amounts of high oxalate content foods is recommended.  In addition, consuming dairy products or calcium tablets with meals can help decrease oxalate absorption.  Calcium binds oxalate in the food preventing it from being absorbed.  

Calcium Oxalate with hypocitraturia:  Everyone loses citrate into the urine.  Citrate prevents stone from forming. Many people are found to have very low urinary citrate levels (HYPOCITRITURIA).  This is the same citrate or citric acid as is found in orange juice.  After other causes of low citrate are investigated (i.e. renal tubular acidosis and hypokalemia) treatment consists of citrate replacement.  Citrate is sold as calcium, sodium, and potassium citrate.  Potassium citrate is the most preferred form if there is no underlying kidney disease.  Lemon juice is a good source of citrate also.  

Uric Acid/Urate Stones:  Uric acid can come from high meat intake.  Some people with gout also form these type of stones.  Low protein diets can decrease uric acid levels. Decreasing alcohol intake can also be beneficial.