Stone formers may have lower 24-h urine volumes than healthy controls, and increasing fluid intake in patients with a history of stones will decrease stone risk. Increasing fluid intake decreases the concentration of calcium, oxalate, phosphorus, and uric acid in the urine and decreases relative supersaturation of calcium oxalate, brushite, and uric acid [4].

Fluid needs vary between individuals. The daily fluid intake goal needs to be individualized based on a target urine output of at least 2.5 L daily. Extra-renal losses from perspiration, respiration, and stool vary considerably between individuals based on comorbidities, perspiration, occupation, climate, and activity level [5]. Provider considerations in developing individualized daily fluid intake goals include:

Patient strategies in complying with daily fluid intake goals include:

The average sodium intake of Americans is estimated to be about 3,000 mg/day or about double the Dietary Reference Intake of 1,500 mg for ages 9–50. After age 50 and up to age 70, daily sodium requirement is 1,300 mg and lowers further after age 70–1,200 mg. High dietary sodium intake can increase urinary calcium excretion, thus increasing the potential for the formation of calcium-containing stones such as calcium oxalate stones. Sodium expands the extracellular volume and competes with calcium ions for reabsorption in the renal tubule. High sodium intake thus leads to increased sodium being reabsorbed in the renal tubule, leading to increased excretion of calcium [5]. High sodium intake has been shown to lead to increased risk of cystine stones and greater urinary saturation of brushite and monosodium urate. High sodium intake also has the ability to decrease urinary excretion of citrate, an inhibitor of calcium oxalate stone formation [6].

About 75 % of salt intake in the US comes from salt added during processing or manufacturing, not salt added at the table or during cooking. Foods with high sodium content include processed and packaged foods such as deli meats, frozen and canned meals, and certain condiments (e.g., soy sauce). Many people eat bread multiple times daily, and with 200–300 mg sodium per slice, bread is frequently a major source of daily sodium. In contrast, fresh meats, legumes, unprocessed whole grains, fruits, and vegetables are naturally low in sodium. The salt shaker is generally a much smaller contributor to daily sodium intake than processed foods [5]. When buying packaged foods, instruct patients to look for foods that are “sodium free” or “salt free” or “low sodium.” Purchasing “reduced sodium” options is helpful but does not guarantee that a food is actually low in sodium. Reduced sodium merely means the food has 25 % less sodium than regular version (Table 2.2).