Most Philadelphia property owners know their water and sewer bills come from the Philadelphia Water Department (PWD). What fewer realize is that buried in that bill is a separate stormwater management charge — one that's calculated differently than your water usage and that can be reduced significantly if you take the right steps. For commercial and multifamily investors, this charge can run hundreds to thousands of dollars per year and is often overlooked in operating cost projections.
This guide explains exactly how Philadelphia's stormwater fee works, how PWD calculates your bill, what credits and grant programs are available to reduce it, how to dispute an incorrect assessment, and what buyers and investors should know before closing.
Bottom line upfront: Philadelphia's stormwater fee is based on the amount of impervious surface on your property — roofs, driveways, patios, and paved areas that prevent rainwater from soaking into the ground. More impervious surface = higher fee. Green infrastructure like rain gardens, green roofs, and pervious pavement can earn credits that reduce your charge by up to 100% on the impervious portion.
When rain falls in Philadelphia, water that can't soak into the ground runs off impervious surfaces — roofs, parking lots, sidewalks, driveways — into the city's combined sewer system. That system carries both sewage and stormwater to PWD's treatment plants. During heavy rain events, the volume of stormwater overwhelms the system, causing combined sewer overflows (CSOs) directly into the Delaware and Schuylkill Rivers. Managing and reducing CSOs is a federally mandated requirement under Philadelphia's Long-Term Control Plan.
The stormwater management fee funds this work. It appears on your PWD bill as a separate line item and is charged to every developed property in Philadelphia — whether or not the property uses city water or sewer service for other purposes.
Philadelphia's stormwater charge has two parts, calculated independently:
The Gross Area Charge is based on the total area of your parcel — the full lot size. It does not distinguish between paved and unpaved areas. Every developed lot pays a GAC. The rate is expressed per 1,000 square feet of gross parcel area. This charge is relatively small for typical residential rowhouse lots (usually $2–$8/month for a 1,500–3,000 sq ft lot).
The Impervious Area Charge is where most of the stormwater fee comes from, and it's the part you can influence. It's based on the total impervious surface area on your property — everything that water can't soak through: roofs, paved driveways, concrete patios, sidewalks on private property, and any other hard surfaces. The IAC rate is expressed per 1,000 square feet of impervious area and is significantly higher than the GAC rate.
| Charge Component | What It's Based On | Can You Reduce It? | Typical Range (residential) |
|---|---|---|---|
| Gross Area Charge (GAC) | Total parcel area (sq ft) | No — fixed to lot size | $2–$10/month |
| Impervious Area Charge (IAC) | Impervious surface area (sq ft) | Yes — via GSI credits | $5–$25/month (residential); $50–$500+/month (commercial) |
PWD updates rates periodically. Current GAC and IAC rates are published on PWD's stormwater billing page at phila.gov/water. Your exact charges depend on current rates and your property's measured impervious area. Check your bill or your PWD account online at mypwdbill.com to see your current assessed impervious area.
PWD determines the impervious area for each Philadelphia property using aerial and satellite imagery combined with geographic information system (GIS) analysis. Analysts identify rooftops, paved surfaces, and other impervious cover from overhead imagery and calculate the square footage attributable to each parcel.
This process is reasonably accurate for most properties, but errors occur — particularly for:
Philadelphia offers significant stormwater fee reductions to property owners who install green stormwater infrastructure (GSI) — practices that capture, infiltrate, or evapotranspire stormwater on-site before it enters the city's sewer system. GSI credits apply only to the Impervious Area Charge; the Gross Area Charge is not reducible.
Credits are calculated based on the volume of stormwater managed by your GSI installation relative to the total runoff from your impervious area. The maximum credit is 100% of the IAC — meaning properties with robust GSI can eliminate the impervious charge entirely.
| GSI Practice | How It Works | Typical Credit Range | Best For |
|---|---|---|---|
| Rain garden / bioretention | Planted depression captures runoff from roof or paved area; infiltrates into soil | 30–80% IAC reduction | Properties with yard space; rowhouse rear yards |
| Green roof (extensive) | Vegetated roofing layer absorbs rainfall, reduces and delays roof runoff | 20–50% IAC reduction | Flat-roof properties; commercial buildings |
| Green roof (intensive) | Deeper soil profile supports larger plantings; greater stormwater retention | 40–70% IAC reduction | Large flat roofs; can support gardens, terraces |
| Pervious pavement | Permeable surface allows water to infiltrate through pavement into stone base | 25–60% IAC reduction | Driveways, parking areas, rear yard paving |
| Cistern / rain barrel (large) | Captures roof runoff for reuse; reduces runoff volume entering sewer | 10–30% IAC reduction | Any property with roof drainage access |
| Tree trench / silva cell | Underground structural cells support street trees that capture and infiltrate runoff | Varies by installation | Commercial streetscapes; larger developments |
GSI credit applications are submitted to PWD's stormwater program. PWD reviews the design, verifies the installed practice meets technical standards, and issues a credit decision. Credits are applied annually to your bill and must be recertified periodically to confirm the GSI installation remains functional.
Installing GSI doesn't just reduce your stormwater bill — Philadelphia offers direct financial assistance programs that can cover most or all of the installation cost.
SMIP provides grants to private property owners who install qualifying GSI practices. Grant amounts are based on the volume of stormwater managed per billing cycle and the type of installation. SMIP is particularly well-suited for small commercial properties, multifamily buildings, and large residential lots where a rain garden or green roof is feasible. Applications are submitted through PWD's Green Stormwater Infrastructure office. Note: SMIP funding is competitive and subject to availability — apply early in each program cycle.
GARP is a performance-based program in which PWD pays private property owners for stormwater management services delivered by installed GSI. Property owners receive ongoing annual payments proportional to the stormwater volume managed, rather than a one-time grant. GARP is typically better suited to larger parcels — commercial properties, parking lots, industrial sites — where the GSI installation manages substantial stormwater volume. GARP agreements run for 20 years and are recorded against the property deed.
GARP and property transfers: Because GARP agreements are deed-recorded, they transfer with the property at sale. If you're buying a commercial or industrial property, check whether a GARP agreement is in place — it carries ongoing maintenance obligations and PWD oversight requirements that the buyer will inherit. This should be disclosed in the sale and reviewed by your attorney.
PWD periodically runs pilot programs targeting specific neighborhoods or infrastructure challenges — for example, combined sewer overflow reduction in specific drainage zones. Pilot programs may offer enhanced grant funding or streamlined approval for properties in priority areas. Check phila.gov/water for current program availability.
Your current impervious area assessment and billing details are available through PWD's online account portal. Here's how to check:
If you believe PWD has overstated your impervious area — for example, because a driveway has been removed, a patio has been replaced with landscaping, or the parcel boundary in PWD's system is incorrect — you can file a stormwater billing adjustment request.
The dispute process involves:
Tip for rowhouse owners: Philadelphia rowhouses have virtually 100% impervious coverage — the building footprint covers most or all of the lot, with minimal permeable area. For a standard 16×50 ft rowhouse on a 16×60 ft lot, your impervious area is typically 900–960 sq ft. The stormwater fee impact is modest for residential rowhouses. Where it matters significantly is for properties with large driveways, rear parking pads, or large flat roofs — and especially for commercial and multifamily properties.
For investors and commercial property owners, the stormwater fee is a material operating cost that deserves inclusion in due diligence and underwriting.
A 10-unit apartment building on a 4,000 sq ft lot with 3,500 sq ft of impervious area (roof + parking) may pay $80–$150/month in stormwater charges. That's $960–$1,800/year — not enormous, but real. Factor it into NOI calculations along with water and sewer costs. For buildings with rear parking pads, converting some paved area to a rain garden may yield a meaningful IAC reduction and qualify for SMIP grant funding to cover installation.
Large-footprint commercial properties — retail, office, warehouse, light industrial — with extensive paved parking or large flat roofs can face stormwater charges of $500–$5,000+/month. At that scale, a GSI investment with GARP or SMIP funding becomes highly economic: the annual stormwater savings plus GARP payments can generate a positive return on the GSI installation within 5–10 years, and the installation adds a long-term operating cost advantage.
Industrial properties with large impervious footprints — warehouses, distribution centers, former manufacturing sites — often have some of the highest stormwater fees in the city. Redevelopment plans for brownfield sites should account for existing stormwater charges and model the fee reduction achievable through GSI integration in the development design. Designing GSI in from the start is far cheaper than retrofitting after construction.
Stormwater fees are a property-level charge, not a lien, and they transfer to the new owner at settlement. There are no special disclosure requirements specific to stormwater fees in Pennsylvania real estate transactions, but savvy buyers and their agents should include stormwater costs in operating expense verification for income-producing properties.
Key due diligence steps for buyers:
Run a free Flagstone report to check permit history, L&I violations, and PWD-related records for any Philadelphia address.
Check This Address Free →No. Your PWD bill includes separate charges: water usage, sewer usage, and stormwater management. The sewer charge is based on water consumption. The stormwater charge is based on impervious area and is independent of how much water you use.
Vacant undeveloped lots have minimal impervious area and therefore minimal stormwater charges — often just a small GAC. Once a lot is developed (building constructed, paved), the charges increase based on the new impervious area.
Individual condo units typically share a single PWD account for the building. The stormwater charge is calculated at the building/parcel level and is typically included in common charges or association fees rather than billed to individual unit owners.
Small residential rain barrels (50–100 gallon) typically don't qualify for meaningful GSI credits under PWD's program — the managed stormwater volume is too small relative to the total runoff from the property. Larger cisterns (500+ gallons) may qualify. For residential rowhouses where the stormwater fee is already modest ($10–$20/month), the credit value rarely justifies the installation cost unless you're pursuing it for sustainability reasons or as part of a broader landscaping project.
Unpaid stormwater charges accrue on your PWD account and are subject to the same collection process as unpaid water and sewer charges. Delinquent PWD accounts can result in service shutoffs and, ultimately, municipal claims against the property. PWD water liens are super-priority — they stand ahead of mortgage debt in the lien hierarchy. See our water and sewer lateral guide for more on PWD lien priority.