Borehole Water for Pools: Filling and Topping Up

Using a borehole to fill or top up a swimming pool is one of the most popular reasons Johannesburg homeowners look into drilling. Municipal water is expensive, and a pool loses hundreds of litres to evaporation every week during a Highveld summer. On paper, a borehole sounds like the obvious answer. In practice, it can work very well — but borehole water is not the same as tap water, and skipping the testing step creates expensive problems.

Why Johannesburg homeowners consider borehole water for pools

The motivation is straightforward. Johannesburg Water’s non-revenue water loss sits at 44.8% according to audited 2024/25 figures, and the municipal network operates with roughly 27 hours of citywide storage buffer. That combination means supply interruptions are real, water pressure varies, and municipal tariffs continue rising. A pool that holds, say, 50 000 litres needs refilling from scratch after a drain-and-clean, then constant top-ups through the evaporation season. For a household already exploring borehole drilling options for garden or household use, extending that supply to the pool feels like an efficient step.

It often is — but only if the water chemistry cooperates.

The chemistry problem: what borehole water typically contains

Unlike municipal water, which is treated to meet SANS 241 (the 2024 South African drinking-water quality standard) before it reaches your tap, borehole water arrives untreated. What it contains depends entirely on the geology it has passed through.

In many parts of Johannesburg — particularly across the dolomite-rich and quartzite geology of the southern and western suburbs — borehole water commonly carries:

• Iron and manganese. These are the main offenders for pool owners. Even modest iron concentrations can oxidise when chlorine is added, turning pool water brown or green and staining plaster, grout, and pool fittings a rust-orange. Manganese stains tend to go purple-black and are notoriously difficult to remove.
• High hardness (calcium and magnesium). Hard water pushes your Langelier Saturation Index into scaling territory, causing white calcium deposits on tiles and fittings.
• Variable pH. Borehole water can be significantly more acidic or more alkaline than your pool wants. Either extreme corrodes equipment or clouds the water.
• Silica and sediment. Can cloud water and stress pool filters.
• Sulphates or hydrogen sulphide. Less common but not rare; sulphide gives water a rotten-egg smell and can interfere with chlorination.

None of these are reasons to rule out borehole water automatically. They are reasons to test first.

Test before you fill — not after

This is the single most important practical point. Get a full water-quality analysis done on your borehole before any water enters the pool. A basic pH and hardness strip is not sufficient. You want a laboratory analysis that covers iron, manganese, total dissolved solids (TDS), pH, total hardness, sulphates, and ideally nitrates. Your pool shop or a water-testing laboratory can advise on sample collection.

If iron comes back above roughly 0.3 mg/L (the SANS 241 guideline for drinking water, used here only as a reference point), you should expect staining risk in a chlorinated pool. As a rough guide, iron above that threshold almost always warrants pre-treatment before the water contacts pool surfaces or chlorine.

Manganese is similarly problematic at very low concentrations. Confirm any thresholds with a pool professional or water-treatment specialist, not just a pool shop’s generic advice.

Treatment options if your borehole water has issues

If testing reveals problems, you have a few routes:

Oxidation and filtration before the pool. A dedicated iron-removal filter or greensand filter on the borehole line oxidises dissolved iron and manganese and removes them before water reaches the pool. This is the cleanest long-term solution if you plan to use borehole water regularly. It adds cost and complexity, but it protects a much larger investment — the pool itself.

Sequential fill and balance. Some pool professionals recommend filling the pool with borehole water slowly, testing at intervals, and correcting chemistry in stages rather than dumping 50 000 litres in and then trying to fix the result. This gives you more control and earlier warning.

Sequestering agents. Chelating or sequestering chemicals can bind iron and manganese ions in the water, keeping them in suspension so the filter removes them rather than letting them oxidise and stain. This works as an ongoing maintenance measure when iron levels are low to moderate, but it is not a substitute for pre-filtration when levels are high.

Blending with municipal water. For top-ups rather than full fills, blending borehole water with municipal supply dilutes problem minerals and is often the simplest approach for routine evaporation losses.

Unsure whether your borehole water is pool-safe before you connect it? Compare 3 free quotes — vetted installers, no obligation.

Practical considerations for connecting a borehole to your pool

Assuming your water tests acceptably, or you have treatment in place, the physical setup is relatively straightforward. The borehole pump feeds water to a holding point or directly to the pool fill line. You will want:

• A non-return valve on the borehole line to prevent pool water back-siphoning into the borehole casing.
• A dedicated fill tap or float valve so the pool fills automatically to a set level without overflow — useful for topping up after evaporation without manual monitoring.
• Flow rate awareness. Most residential borehole pumps are sized for garden or household use; confirm with your installer that the pump and borehole yield can sustain pool-filling volumes without running the aquifer dry. Typical complete borehole systems in Johannesburg run R40,000–R150,000, with most falling between R60,000 and R100,000, depending on depth and pump specification.

If you are drilling specifically and primarily for irrigation rather than pool use, it is worth reading the guidance on borehole systems designed for irrigation-only applications before specifying your pump and casing diameter.

Ongoing maintenance differences with borehole-filled pools

Even after a clean initial fill, you will likely find that pool chemistry behaves differently with borehole water making up your top-ups. A few things to anticipate:

• More frequent testing. Without municipal pre-treatment, mineral composition can vary seasonally as water table levels change. Test water chemistry weekly rather than fortnightly.
• Higher chemical consumption initially. Hardness, TDS, and pH corrections will be needed more often until the pool water stabilises over a season.
• Filter maintenance. Higher sediment loads from untreated borehole water mean backwashing your sand or cartridge filter more regularly.
• Chlorine demand. Iron and organic matter in borehole water can increase chlorine consumption because chlorine oxidises those compounds first before becoming available as a sanitiser. You may notice higher than expected chlorine usage in the first season.

None of this is unmanageable — it simply means adjusting your maintenance routine and budget expectations accordingly.

Ready to get properly sized quotes for a borehole that works for your pool and your property? Request quotes from vetted local drillers — free, no obligation.

Making the decision: is it worth it?

For most Johannesburg homeowners with a pool, using borehole water for filling and top-ups makes long-term financial sense — provided the geology cooperates and the water is tested first. The upfront system cost is significant; as a rough guide, comparing multiple installation quotes properly before committing makes a material difference to what you pay and what you get.

The honest case against is this: if your borehole produces water with high iron or manganese and you do not install pre-treatment, you will stain your pool. Replastering and tile replacement are expensive. The cost of a proper lab water test and, if needed, an iron-removal filter is far smaller than the cost of putting right a stained pool interior.

Test first, treat if needed, connect with the right equipment, and borehole water for your pool becomes a reliable, cost-effective alternative to running your municipal meter every summer.