In This Article
The Setup — What We Were Working With
500-gallon HDPE tank on a timber stand 28 feet above the cabin floor. 28 ft elevation = 12.1 PSI at the cabin floor (28 ÷ 2.31). Spring-fed from a hillside collection box 180 feet away, 15 feet above the tank — passive gravity fill, no pump anywhere in the system.
Distribution points: kitchen sink, bathroom sink, outdoor wash station. No indoor shower (we use an outdoor solar shower). Total material cost for the gravity system: $398.
The Full Materials List
| Item | Cost |
|---|---|
| 500-gallon HDPE tank (used, food-grade, local farm) | $140 |
| 4×4 treated lumber (16 boards, 8-ft each) for tank stand | $85 |
| 3/8″ carriage bolts, lag screws, structural hardware | $22 |
| 3/4″ polyethylene pipe (200 ft roll) | $48 |
| Push-fit fittings (elbows, tees, ball valves) | $31 |
| Inline sediment filter housing + cartridge | $24 |
| Brass ball valves (3) | $27 |
| Pressure gauge | $9 |
| Overflow pipe fittings | $12 |
| Total | $398 |
Building the Tank Stand
Four posts of 4×4 treated lumber at 8 ft above grade (the slope gives us the remaining 20 ft of effective elevation above the cabin). Double 2×8 beams across the top, cross-braced with 2×6 diagonal braces on all four sides.
Full weight calculation: 500 gal × 8.34 lb/gal = 4,170 lbs. We over-engineered deliberately — the stand is rated for well over that.
Mistake we made: didn’t account for the cantilever load when the float valve closes and the tank fills from one side. The float valve side pulled the tank slightly off-level. We added a diagonal corner brace after the fact. Build the bracing before installing the tank.
Plumbing the System
Tank outlet: 1″ polyethylene from tank, reduced to 3/4″ main, 1/2″ branches at each fixture. Sediment filter: 20-micron cartridge housing on the outlet line, before the distribution tee inside the cabin.
Measured pressure at kitchen sink: 10.8 PSI (slightly below our calculated 12.1 PSI — expected; pipe friction losses over a 150 ft run account for the difference). Float valve in the tank maintains level from the spring collection box automatically.
Six Months of Operation — What Works, What Doesn’t
Works Well
- Zero maintenance on the pipe runs in 6 months
- Sediment filter: replaced once in 6 months (spring water is relatively clean)
- Flow rate at kitchen sink: fills a 1-gallon pot in 90 seconds — adequate for all cooking and washing
- The spring has never run low — output comfortably exceeds demand year-round
What We’d Do Differently
- Better spring collection box: the screened inlet needs a finer screen — insects got into the tank during summer
- Second shutoff valve at the house entry: currently have to hike to the tank to fully shut off water; an inline ball valve at the cabin entry would fix this
- Upsize the main pipe to 1″: 3/4″ main is borderline when kitchen and bathroom sinks run simultaneously; noticeable pressure drop
Water Quality
Spring water tested: zero coliform, pH 7.2, hardness 145 mg/L (moderately hard). No treatment needed for bathing and washing. We added a Big Berkey gravity filter at the kitchen counter for drinking and cooking water — the spring water tastes excellent through it. Total drinking water filtration cost: $285 one-time for the Berkey.
Complete Water System Cost Summary
| Component | Cost |
|---|---|
| Gravity distribution system | $398 |
| Big Berkey drinking filter | $285 |
| Spring collection box (separate build) | $65 |
| Total water system | $748 |
$748 for full-time water supply for 2 people — kitchen, bathroom, washing. No ongoing electricity cost. No pump maintenance. No pressure tank to replace.
More Detailed Guides
- Gravity Water System Guide — the technical deep-dive on pressure, pipe sizing, and tank placement
- Water Filtration Guide — choosing the right filter for your water source
- Big Berkey Review — our drinking water filter
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