An LMN is the single document that turns a water filter from a personal expense into a qualified HSA/FSA medical expense. Here is what it is, why you need it, and how to get one without a separate doctor's visit.
A Letter of Medical Necessity is a short statement from a licensed provider confirming that a product is needed to treat, mitigate, or prevent a specific medical condition. It does for a water filter what a prescription does for a medicine: it satisfies the IRS requirement that an expense be medical rather than personal. The framework comes from IRS Publications 502 and 969.
Ordinary filtration is considered a personal, general-health expense — not reimbursable on its own. The LMN supplies the missing link: it documents that your filter addresses a health condition (for example, reducing exposure to lead, PFAS, or nitrates, or protecting an immunocompromised household). With that documentation, the purchase qualifies.
You do not need to book an appointment and explain water chemistry to your doctor. Retailers partnered with services like TrueMed build the process into checkout:
On an eligible SpringWell system, select the TrueMed option.
A couple of minutes, confidential. A licensed provider reviews your responses.
If you qualify, the letter is issued — commonly within a few hours.
Use your HSA/FSA card (split with a regular card if needed) and store the LMN and itemized receipt.
SpringWell's eligible systems issue the LMN through TrueMed at checkout — the cleanest way to keep your timing and documentation correct.
See how it works → Shop eligible systems →A valid LMN is short but specific. Whether a provider writes it directly or a service like TrueMed issues it, it should contain:
Here is a simple template containing those elements. If you obtain your letter through TrueMed at checkout, you do not need to write anything — the provider produces it for you. This is for reference, or for readers working with their own physician.
Date: [on or before purchase date]
To the Plan Administrator:
I am the treating provider for [patient name]. Based on [diagnosis or documented condition — e.g., elevated blood lead level, eczema, immunocompromised status], I recommend a [whole-house water filtration system / reverse osmosis system / UV purifier] as medically necessary to [treat / mitigate / prevent] this condition by reducing exposure to [lead / PFAS / nitrates / waterborne pathogens] in the patient's household water supply.
This recommendation is valid for [duration, e.g., 12 months], including replacement filters required to maintain the system.
Sincerely,
[Provider name, credentials, license number, signature]
Suppose a family in a pre-1986 home tests their tap water and finds lead above the EPA action level, and they have a toddler. Their provider documents the elevated-lead concern, recommends a lead-reducing whole-house system to prevent ongoing exposure to a vulnerable child, and notes the recommendation covers replacement filters for 12 months. That letter, dated before the purchase, turns the system into a qualified medical expense. See how to get a letter and what providers look for.
An LMN is typically valid for up to 12 months for the same product category. That window matters most for replacement cartridges: if you reimburse ongoing replacements, you may need a renewed letter once the original lapses. Set a reminder, keep each letter with the matching receipts, and see how reimbursement works for submission details. When you are ready to buy, our step-by-step purchase guide walks through the whole flow.
Any licensed healthcare provider acting within their scope can issue an LMN — physicians (MD/DO), nurse practitioners, and physician assistants are common examples. With a checkout service, an independent licensed provider reviews your survey, so you do not need an existing relationship. If you go through your own clinic, your treating provider is the natural choice because they already know your history.
People often ask whether they need a "prescription" for a water filter. Not exactly. A prescription orders a specific medication or therapy; a Letter of Medical Necessity explains why a product or piece of equipment is needed to treat or prevent a condition. For durable items like water filters, the LMN is the right instrument, and it is what FSA/HSA administrators expect for equipment.
Some administrators occasionally request additional detail — a diagnosis code, a longer rationale, or a renewal. This is routine. Keep your provider's contact handy, respond promptly, and retain every version of the letter. Because requirements vary between employers and plans, a quick call to your administrator before a large purchase can save back-and-forth later. See how reimbursement works for submission specifics.
The strongest letters are specific rather than generic. A letter that names the documented contaminant (say, lead above the action level) and ties it to a vulnerable household member is more durable than one that vaguely cites "water quality." If you work with your own provider, share your water test results and point them to the template above so the rationale is concrete.
A licensed healthcare provider. With TrueMed, a licensed provider reviews your health survey and issues the LMN if you qualify, so you do not need a separate doctor's appointment.
Often up to 12 months for the same product category, depending on the issuer and your plan, after which you may need to renew. Keep the dated letter with your records.
Generally no. The LMN should be dated on or before your purchase. Retroactive letters are typically not accepted, which is why buying through a checkout that issues the LMN at purchase is the safest route.
