Water Purification and Softening Systems Used in Conjunction with Home Dialysis — NCD 193 | CMS Coverage Update

TL;DR: The Centers for Medicare & Medicaid Services (CMS) modified NCD 193, governing Medicare coverage of water purification and softening systems used with home dialysis equipment, effective March 7, 2026. Here's what changes for billing teams.

CMS's NCD 193 is the National Coverage Determination that controls whether Medicare pays for water treatment systems used alongside home hemodialysis and peritoneal dialysis units. This policy update draws sharper lines around what's covered, what's excluded, and — critically — when a water softening system can slip through the coverage door. No specific HCPCS or CPT codes are listed in the current policy document, but the clinical and billing criteria within NCD 193 directly affect reimbursement for home dialysis supply claims and the medical necessity documentation your team sends to Medicare Administrative Contractors (MACs).

Quick-Reference Table

CMS Home Dialysis Water Purification Coverage Criteria and Medical Necessity Requirements 2026

The core of CMS's NCD 193 coverage policy is straightforward: water used for home dialysis must be chemically free of heavy trace metals and organic contaminants, and as bacteria-free as practical — though it doesn't need to be biologically sterile. Given that most municipal and well water supplies can't meet those standards on their own, Medicare covers a water purification system used in conjunction with either peritoneal or hemodialysis equipment in the home.

Two systems qualify under this coverage policy. Deionization removes organic substances, mineral salts causing hardness, and compounds of fluoride and chloride through filtration and ion exchange. Reverse osmosis (RO) uses pressure to force water through a porous membrane, removing impurities. Either one is considered adequate for home dialysis — and that "either one" designation is where medical necessity gets complicated.

CMS explicitly states that using both a deionization unit and an RO unit in series is medically unnecessary. The logic: each system independently produces water that's chemically and bacteriologically acceptable for dialysis. Billing both as part of a dual-system configuration will not survive MAC review. If your patient's chart or equipment order reflects a tandem setup, expect a claim denial without strong justification for why a single-system approach wasn't used.

Activated carbon filters are covered when used as a component of a water purification system to remove unsafe concentrations of chlorine and chloramines — but only when prescribed by a physician. That physician order requirement isn't optional documentation. Missing it means the claim lacks the medical necessity support CMS requires, and MACs will flag it.

Prior authorization isn't explicitly called out in NCD 193, but MAC development of medical necessity is — which functions similarly in practice. When a water softening system is replaced with a purification unit in an existing home dialysis setup, the MAC will actively request the physician's rationale before approving reimbursement. Treat that as a de facto prior auth process.

CMS Home Dialysis Water Softening System Exclusions and Non-Covered Indications

Water softening systems are excluded from Medicare coverage as not reasonable and necessary under §1862(a)(1) of the Social Security Act — full stop, with one narrow exception.

The reason for the exclusion isn't arbitrary. A water softener doesn't remove hazardous heavy metal contaminants like arsenic. It softens; it doesn't purify. Medicare's position is that a softener alone doesn't meet the clinical standard for home dialysis water quality, so it won't pay for one as a standalone dialysis system component.

The narrow exception: a water softening system may be covered when it's used specifically to pretreat water entering an RO unit. Three conditions must all be met simultaneously:

The softener doesn't need to be physically built into the RO unit. But it must function as an integral part of the dialysis system, not as a standalone household appliance that happens to also serve the dialysis setup. That distinction matters at the claim level. If a MAC audits and finds the softener is servicing the whole house — or can't find documentation proving it isn't — the claim dies.

Spare deionization tanks are also specifically excluded. CMS classifies them as a precautionary supply rather than a current treatment requirement. Stocking a backup tank is clinically reasonable, but Medicare won't pay for it.

Coverage Indications at a Glance

CMS Home Dialysis Water Purification Billing Guidelines and Action Items 2026

If you're managing a large home dialysis program or a DME supplier book with significant home dialysis volume, loop in your compliance officer to review current documentation standards against these criteria before the March 7, 2026 effective date.

CPT, HCPCS, and ICD-10 Codes for Home Dialysis Water Purification Under NCD 193

A Note on Codes for NCD 193

The policy document for NCD 193 does not specify particular CPT, HCPCS Level II, or ICD-10-CM codes. This is not unusual for older NCDs that were written before current coding frameworks. In practice, home dialysis water purification and softening systems are billed through HCPCS codes assigned by your MAC or established through the DME fee schedule — your MAC's local billing guidance will be the authoritative source for the specific codes your region uses.

Do not treat the absence of codes in this NCD as flexibility to bill creatively. CMS's coverage criteria in NCD 193 govern what's billable regardless of which HCPCS code the item falls under. The medical necessity rules apply to the equipment category, not just specific codes.

Contact your MAC or your DME billing consultant to confirm which HCPCS codes map to deionization systems, RO units, activated carbon filters, and water softeners in your jurisdiction. Then apply the NCD 193 coverage criteria to those codes in your charge capture and documentation workflows.