Distilled water is devoid of most toxins but also devoid of minerals that are essential for human health. Someone with kidney disease should have a prescription for the amount of water and minerals they are able to tolerate.
The process of distillation removes solutes and most toxins including heavy metals and radionuclides, and it kills viruses and bacteria (Conti 2005). However, distillation also removes essential minerals that are naturally found in water including calcium, magnesium, sodium, selenium, fluoride, sulfate, chloride, iron, zinc, and lithium (Vema 2014, Quattrini 2016). Tap water may also contain significant amounts of calcium, magnesium, and sodium, minerals that are then removed during distillation (Azoulay 2001).
Drinking distilled water shouldn’t deplete significant amounts of minerals from the body but cooking with demineralized water (including “softened” water) may cause loss of nutrients from food. Therefore, it’s especially important to obtain these minerals from other sources including foods and supplements if needed. Researchers suggest that consumption of “hard” mineral-rich water, especially that containing magnesium, may reduce the risk of cardiovascular disease, motor neuronal disease, and pre-eclampsia (Verma 2014).
Drinking distilled water should not negatively affect the kidneys specifically, but it’s important to consume adequate minerals from other sources. In the event of kidney disease, a lower mineral intake may be desirable depending on kidney function (the kidney excrete excess minerals when they are functioning properly). A renal specialist should create an individualized prescription for the amount and type of water and minerals allowed during the various stages of kidney disease.
References
Azoulay, A et al. “Comparison of the mineral content of tap water and bottled waters.” Journal of general internal medicine vol. 16,3 (2001): 168-75. doi:10.1111/j.1525-1497.2001.04189.x
Conti, Aldo. "Distilled water." Water encyclopedia 4 (2005): 441-442.
Kozisek, Frantisek. "Health risks from drinking demineralised water." Nutrients in drinking water 1.1 (2005): 148-163.
Verma, K C, and A S Kushwaha. “Demineralization of drinking water: Is it prudent?.” Medical journal, Armed Forces India vol. 70,4 (2014): 377-9. doi:10.1016/j.mjafi.2013.11.011
Quattrini, Sara et al. “Natural mineral waters: chemical characteristics and health effects.” Clinical cases in mineral and bone metabolism : the official journal of the Italian Society of Osteoporosis, Mineral Metabolism, and Skeletal Diseases vol. 13,3 (2016): 173-180. doi:10.11138/ccmbm/2016.13.3.173