On acreage around Mocksville, Welcome, Stokesdale and much of rural Randolph County, the water that fills the pool comes out of the ground. That is fine, but it is not the same water a Greensboro pool gets from the tap.
What well water brings with it
- Iron. The most common problem locally. Dissolved iron is invisible in the well, and it oxidizes as soon as chlorine hits it. That is where the brown or rust-colored staining comes from.
- Manganese. Less common, more stubborn. Produces dark brown to black staining that is difficult to remove once it sets.
- Copper. Sometimes from the water, sometimes from plumbing. Produces blue-green staining.
- Hardness. Calcium and magnesium. Too high causes scale on the finish and equipment; too low pulls calcium out of the plaster itself.
- Variable pH and alkalinity, which affects everything else.
Test before you fill, not after
A water test on the well before the fill costs very little and tells you exactly what you are dealing with. Once a pool is full and stained, the options are chemical treatment, acid washing, or living with it — all worse than prevention.
If iron or manganese is present at any meaningful level, a sequestering agent goes in with the fill and continues as part of regular maintenance. It holds the metals in solution so they cannot deposit on the finish.
Filter the fill if the numbers are bad
Where levels are genuinely high, filling through a hose-mounted iron filter is worth the cost and the extra time. It is slower, and it is dramatically cheaper than remediating a stained new plaster finish.
Hardness cuts both ways
Very hard well water leads to scale — cloudy water, rough deposits at the waterline and on heater elements. Very soft water is aggressive and etches plaster, which is a slower problem but a more expensive one.
Both are managed, and both need to be known before the pool is filled rather than discovered in the second season.
Ongoing, not just at fill
Every top-up brings the same water. Evaporation in a Piedmont July is significant, so a well-filled pool receives a meaningful amount of new well water every summer. Sequestering and hardness management are ongoing tasks, not a one-time step.
The short version
Test the well, treat the fill accordingly, and keep sequestering as part of the routine. Done that way, well water makes a perfectly good pool.
The fill itself takes longer than people expect
A residential well typically produces a fraction of what a municipal tap does, and filling a pool is a large volume. Running a well flat out for a day or more risks drawing the water level down, pulling in sediment, and in a bad case damaging the pump.
The practical approach is filling in stages over several days, or bringing in water by truck for the bulk of the fill and topping up from the well. Water delivery costs money and it is considerably cheaper than a well pump.
It also matters that a pool should be filled continuously once started rather than in long stops and starts, because a partially filled new plaster pool with a waterline sitting at one level for days can leave a mark. Coordinate the plan with your builder rather than improvising it.
Sediment and the first filter cycle
Well water frequently carries fine sediment that municipal water does not. The filter will catch a great deal of it in the first days, and pressure will climb faster than normal. Expect to clean the filter early in the life of the pool and do not read it as a fault.
Retesting after the season
Well water chemistry is not static. It changes with rainfall, with drought and as the aquifer level moves through the year. A test in spring and another in late summer tells you whether what you are adding still matches what is coming out of the ground.
Drought years in particular tend to concentrate minerals, so a well that was unremarkable in a wet spring can produce noticeably harder or more metallic water in a dry August.
Softened water is not the answer
Homeowners with a household softener sometimes ask about filling from it. It is generally a poor idea: softened water is low in calcium, and water low in calcium hardness is aggressive toward plaster. It also adds sodium, and it puts an enormous load on the softener. Fill from raw well water and manage the hardness in the pool.