Commercial RO System Sizing Calculator — What Size (GPD) Do You Need?

Frequently Asked Questions

What does GPD mean?

GPD stands for gallons per day — the standard unit for rating commercial RO membrane and system output. A 2,500 GPD system produces 2,500 gallons of purified permeate water over a 24-hour operating period at rated temperature, pressure, and feed water TDS. Most commercial systems are designed to run 20–22 hours per day, so a 2,500 GPD rating works out to roughly 113–125 gallons per hour of continuous output.

How many GPD do I need for my business?

Start by estimating your total daily water consumption for every process that will use RO-treated water — cooking, beverage production, rinsing, equipment washing, etc. Then add 15–20% headroom for growth and peak days. If your daily demand is 1,800 gallons, a 2,500 GPD system with a 400–500 gallon storage tank is a common fit. The GPD quick-reference table above maps common applications to GPD class — use it as a starting point, then refine with a source water test.

How do I size a commercial RO system?

Size a commercial RO system by working through seven variables in order: (1) total daily water demand in GPD, (2) peak-hour demand, (3) source water TDS and hardness, (4) required recovery rate, (5) storage tank volume, (6) available feed pressure, and (7) pretreatment requirements. See the step-by-step sizing guide above. The most common mistake is sizing to average daily demand without accounting for peak-hour bursts — which results in a system that can't keep the storage tank full during your busiest hours.

Does TDS affect which size RO system I need?

Yes — significantly. RO membranes are rated at a standard TDS (typically 500–2,000 ppm depending on the membrane type). High-TDS feed water increases osmotic pressure, which reduces membrane flux (output per membrane). A system rated at 2,500 GPD on 500 ppm municipal water may deliver only 1,800–2,000 GPD on 2,000 ppm well water without additional membrane stages or a higher-pressure pump. Always test your feed water TDS before finalizing system size.

Does feed water pressure affect RO output?

Yes. RO membranes require adequate net driving pressure (NDP) to push water through the membrane against osmotic resistance. Most commercial membranes require a minimum of 60–80 PSI feed pressure; high-rejection membranes may need 100–150 PSI or more. Low feed pressure reduces output and recovery rate. If your municipal supply or well pump delivers less than 60 PSI at the RO inlet, a booster pump is required — factor that into your budget and pretreatment plan.

How much reject (waste) water does a commercial RO system produce?

Commercial RO systems typically recover 50–75% of feed water as purified permeate. The remaining 25–50% exits as reject water (concentrate), which carries the dissolved solids removed from the product water. To produce 2,500 GPD of treated water at 65% recovery, you need approximately 3,850 GPD of feed water, and roughly 1,350 GPD goes to drain. Plan for drain capacity accordingly. The EPA notes that older residential RO units can waste 5 or more gallons per treated gallon; WaterSense-certified units are held to a 2.3:1 waste ratio or better.

Do I need a storage tank with a commercial RO system?

For almost all commercial applications, yes. RO systems produce purified water at a steady, controlled rate around the clock — they cannot ramp up output on demand during peak periods. A storage tank acts as a buffer: the RO system fills it continuously, and your processes draw from it at whatever rate they need. A typical sizing rule is to maintain 20–30% of your daily demand in storage — so a facility using 3,000 GPD would size for a 600–900 gallon storage tank. Without adequate storage, peak demand will exceed instantaneous RO output and you'll pull untreated water or lose pressure.

What size RO system does a restaurant need?

A small café or coffee shop (up to 50 seats) typically needs a 500–750 GPD commercial RO system. A full-service restaurant with 50–150 seats and a full kitchen — including dishwashing, cooking water, and ice — typically requires 750–2,500 GPD. Higher-volume restaurants or those with large ice production may need 2,500–4,000 GPD. Always account for your peak lunch or dinner service window, not just the daily average. The Crystal Quest Mid-Flow RO (500–7,000 GPD) covers the full restaurant range.

What size RO system does a coffee shop need?

Specialty coffee shops care about both volume and water chemistry — RO-treated water with remineralization is the gold standard for espresso extraction and consistent brewing. A coffee shop producing 200–400 drinks per day typically needs 300–600 GPD of RO water. A high-volume cafe or multi-location roaster operation may need 750–1,500 GPD. The 500 GPD variant of the Mid-Flow RO is the most common fit for a single café location.

What size RO system does a car wash need?

Spot-free rinse arches are the primary RO application for car washes. A touchless or conveyor car wash with 5–10 bays typically consumes 1,000–3,000 GPD for the final rinse stage. Self-serve bays (where customers control rinse time) are harder to estimate but 500–1,500 GPD per active bay is a workable rule of thumb. Size to peak-day throughput, not average — a car wash on a Saturday afternoon can use more water in 4 hours than on a Monday all day. The Mid-Flow RO (1,500–4,000 GPD) covers most car wash applications.