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Whole House RO: Sizing, Cost & Storage Tanks
Everything you need to size and build a whole house RO setup: the whole house reverse osmosis system itself (300 to 7,000 gallons per day), atmospheric storage tank and repressurization pump kits, remineralizers, replacement membranes and pre-filter cartridges. Built and tested in the USA by Crystal Quest, shipped free by freight. Sizing by household, real costs, storage tanks and well-water pre-treatment are below the products.
Whole house RO: what it does and who needs one
A standard under-sink RO makes a few gallons a day for drinking. A whole house RO system makes hundreds or thousands of gallons a day and feeds every fixture, so showers, laundry, ice makers and the water heater all run on purified water. It is the only residential treatment that removes dissolved contaminants across the board: arsenic, fluoride, nitrates, sodium, PFAS, lithium, uranium and high total dissolved solids, the things softeners and carbon filters can't touch.
Most homes don't need one. Whole house RO earns its cost when a well test shows a dissolved contaminant above the health limit, when TDS is high enough to taste or scale everything, when a sodium-restricted household is on softened water, or when a home is on brackish or reclaimed supply. If your problem is hardness, iron or bacteria, a softener, iron filter or UV system is the right tool at a fraction of the price, and those often sit ahead of an RO anyway.
The three parts of a whole house RO setup
Because RO production is slow and steady, a whole house setup is three parts working together, and the kit options on the product page reflect that:
- The RO unit: sediment pre-filtration and membranes on a frame. It rejects dissolved solids and sends 50–67% of the feed to drain as concentrate (33–50% recovery).
- An atmospheric storage tank (165, 220 or 550 gallons) that buffers production so you can run a shower and a washing machine at once.
- A repressurization pump and float switches that deliver tank water to the house at normal pressure and cycle the RO unit as the tank draws down.
Choose Standalone if you already own a tank and pump, or Add Storage Tank Kit for the complete package. A remineralizer after the tank is recommended: RO water is slightly acidic and mineral-free, which tastes flat and is aggressive to copper plumbing over years.
Whole house RO sizing: which GPD and tank do I need?
Size by gallons per day of purified water your household uses, plus headroom for laundry and irrigation. A family of four uses roughly 250–400 gallons a day at all fixtures. Your well or supply also has to meet the unit's minimum feed flow.
| System size | Typical home | Storage tank in kit | Where to buy |
|---|---|---|---|
| 200 GPD (off-grid) | Cabin, RV, tiny home, drinking and cooking supply | Portable, no tank | Off-grid portable RO |
| 300–400 GPD | 1–1.5 bathrooms, 1–2 people | 165 gal | Whole house reverse osmosis system |
| 500–2,500 GPD | 1–4 bathrooms; most single-family homes | 220 gal | Whole house reverse osmosis system |
| 4,000–7,000 GPD | 5+ bathrooms, estates, multi-family, irrigation | 550 gal | Whole house reverse osmosis system or commercial RO |
RO storage tanks and repressurization pumps
The storage tank is what makes whole house RO livable. An RO unit producing 1,000 gallons a day only delivers about 0.7 GPM, far below what a shower draws, so purified water collects in an atmospheric (unpressurized) tank and a repressurization pump sends it to the house at normal pressure. Float switches in the tank tell the RO unit when to start and stop. Size the tank to hold at least a day's peak use: 165 gallons for small homes, 220 gallons for most single-family homes, 550 gallons for large homes and multi-family. The tank kit on the product page includes the tank, a 1.5 HP pump and the float switches; choose Standalone if you're reusing an existing tank and pump.
Whole house RO system for well water
Well water is where whole house RO is most often the right answer, because wells are where arsenic, nitrates, uranium, fluoride and high TDS show up. Two rules make or break the install. First, pre-treat: RO membranes are rated for feed water up to about 15 grains of hardness with no iron, manganese or sediment, so on most wells the treatment train is iron filter and/or softener, then RO, then remineralizer, with UV after the tank if bacteria is a concern. Second, check pump capacity: the RO unit's minimum feed flow (1.5 GPM for 500–1,800 GPD, 4 GPM for 2,500, 6–10 GPM for 4,000–7,000) has to be available while the house is also drawing. Send us a water test and we'll size the whole train. For drinking-water-only RO on a well, see RO systems for well water.
How much does a whole house RO system cost?
| Item | Typical range | Notes |
|---|---|---|
| RO unit, standalone | $2,700–$8,500 | 300 GPD to 7,000 GPD |
| Storage tank kit (tank, pump, floats) | +$1,400–$2,500 | 165, 220 or 550 gallon |
| Remineralizer | from $605 | Sized to system (Big Blue for 300–2,500 GPD; 1.5 cu ft for 4,000–5,000); recommended |
| Pre-treatment (softener / iron filter) | $800–$2,500 | Only if your water needs it; protects the membranes |
| Annual upkeep | $100–$300 | Sediment cartridges every 6 months; membranes every 2–3 years |
Prices above are current list pricing, before any storewide discount; installation by a plumber is extra and varies by site. Everything here ships free by freight and we coordinate delivery with you.
Replacement membranes and cartridges
Every system here uses standard-size components, so parts are stocked rather than proprietary: 2.5″ × 21″, 2.5″ × 40″ and 4″ × 40″ freshwater membranes, plus pleated sediment and SMART pre-filter cartridges. The product page lists the exact cartridges and membranes by system size.
Frequently asked questions
Is whole house RO worth it? If a lab test shows a dissolved contaminant you can't remove any other way, or TDS high enough that you're buying bottled water and replacing fixtures, yes. If the complaint is hardness, staining or smell, a softener or iron filter solves it for less and wastes no water.
How much water does it waste? These systems run 33–50% recovery, so one to two gallons go to drain per gallon purified. Concentrate can be routed to irrigation or a dry well where code allows.
Do I need a softener with whole house RO? On hard water, yes. Scale is the main thing that shortens membrane life, and a softener ahead of the RO is cheaper than replacing membranes early.
Will RO water hurt my plumbing? Untreated RO water is mildly acidic and can be aggressive to copper over time. A remineralizer after the tank corrects pH and puts calcium and magnesium back.
Can I add RO to an existing softener and UV? Yes. The RO goes after the softener and before the tank; UV goes after the tank. The schematics on the product page show these complete trains.
Need more than a home can use? See commercial water filtration. Want drinking water only? See under-sink and countertop reverse osmosis. Or call 800-374-2143 and we'll size it from your water test.
