What Size Reverse Osmosis System Do I Need for 6 People?
For 6 people using RO water for drinking and cooking, here's the membrane and tank size that keeps up — and how it changes with heavier use.
For 6 people (drinking & cooking), paired with a 4-gallon storage tank.
| Daily RO water demand | 18 gallons |
|---|---|
| Real-world membrane output | ~50% of rated (at typical temp/pressure) |
| Recommended membrane | 100 GPD |
| Recommended storage tank | 4-gallon |
100 GPD RO System
Best for 5–6 people / heavy use
High-flow membrane for larger families or heavy use (coffee, ice, pets). Often paired with a permeate pump for fast recovery.
How this is calculated
We estimate your household's daily reverse-osmosis water use (drinking, cooking, coffee, ice), then size the membrane against real-world output: a membrane's rated GPD is measured at 77°F and 60 psi, but a typical home gets roughly half that. A safety margin keeps the storage tank ahead of peak demand. We then pick the smallest standard membrane that comfortably keeps up.
The result above assumes standard drinking-and-cooking use. If your household leans on the RO line for a coffee maker, ice maker, pets, or plant watering, switch the usage setting to "heavy" and you'll likely move up a membrane size. A larger storage tank also helps a 6-people home avoid running dry at peak times.
Frequently asked questions
What size reverse osmosis system do I need?
Match the membrane's gallons-per-day (GPD) rating to your household's daily drinking and cooking water, with margin. As a rule of thumb: 1–3 people → 50 GPD, 4–5 people → 75 GPD, 6+ or heavy use → 100 GPD. The calculator above tailors it to your usage.
Does a 75 GPD membrane really make 75 gallons a day?
No — that rating is measured at 77°F and 60 psi. A typical home runs cooler and lower-pressure, so real output is roughly half the rating. That's why we size against real-world output, not the label number.
What size RO storage tank should I get?
Most under-sink systems use a 2.8–4 gallon tank (which holds ~2–3 gallons of usable water). Larger families or higher-GPD membranes benefit from a 4-gallon or dual-tank setup so you don't run the tank dry.
Do more people just mean a bigger membrane?
Mostly. A higher-GPD membrane refills the tank faster so it keeps up with demand. Above ~6 people or heavy use, a permeate pump or a second tank helps more than going to an oversized membrane alone.
Is a 100 GPD RO system enough for 6 people?
For 6 people on standard drinking-and-cooking use, a 100 GPD membrane refills the tank fast enough to keep up. Heavy use (coffee, ice, pets) or low water pressure can warrant the next size up or a permeate pump.