How to Treat Well Water for Pool

Introduction

Using well water to fill your pool is a common practice in Margem Sul, especially in rural areas like Palmela, Moita, and the estates of Azeitão. Well water is free and abundant, but comes with unique challenges that mains water doesn't present.

The main problem with well water is that it contains dissolved minerals – iron, manganese, calcium, and sometimes copper – that aren't visible when the water comes out of the well, but become evident when treated with chlorine. The crystal-clear well water can transform into a brown, green, or cloudy soup within hours of adding chlorine.

In this article, we explain how to analyse well water before use, how to treat the most common minerals, and how to keep pool water clean and healthy when your source is a well. With the correct treatment, well water can be as good as mains water – or even better, as it doesn't contain residual chlorine or fluoride.

Characteristics of Well Water

What Well Water Contains

The composition varies according to local geology, but in Margem Sul the most common contaminants are:

Why Minerals Cause Problems

When water is in the well, minerals are in a "reduced" form – dissolved and invisible. When you add chlorine (an oxidiser), minerals change to "oxidised" form:

Before chlorine:

• Fe²⁺ (ferrous) – soluble, invisible
• Mn²⁺ – soluble, invisible

After chlorine:

• Fe³⁺ (ferric) – insoluble, brown
• MnO₂ – insoluble, black/brown

This is why well water can look perfect until you add chlorine, then transform into brown water within minutes.

Analysis Before Filling

Basic Test (DIY)

Before filling the pool with well water, do this simple test:

1. Collect a sample (1-2 litres in a clean bottle)
2. Add a few drops of bleach (chlorine)
3. Wait 30 minutes
4. Observe changes:

• Water stays clear = low in metals
• Water turns brown = iron
• Water turns black = manganese
• Water turns green = copper

Professional Test

For precise results, have it analysed in a laboratory:

What to Test

Essential:

• Total iron
• Manganese
• Hardness (calcium + magnesium)
• pH
• Alkalinity

Recommended:

• Copper
• Sulphates
• Total dissolved solids (TDS)
• Nitrates (if near agriculture)

Iron Treatment

Symptoms of Iron in Water

• Brown or orange water after chlorination
• Rust stains on walls and floor
• Blonde hair turns orange
• Filter clogs rapidly
• Water with metallic taste

Method 1: Metal Sequestrant

The sequestrant "captures" metals and prevents them from staining:

How it works:

• Binds to metal ions
• Keeps them in solution
• Prevents oxidation and precipitation
• Requires regular reapplication

Application:

1. Add before chlorinating
2. Dose: 30-50ml per m³ (as per product)
3. Let circulate 2-4 hours
4. Then add chlorine gradually

Advantages:

• Easy to use
• Doesn't remove metals (just "hides" them)
• Quick solution

Disadvantages:

• Temporary effect (2-4 weeks)
• Requires reapplication
• Metals are still in water

Method 2: Oxidation and Filtration

Removes metals permanently:

Process:

1. Oxidise – Add high dose chlorine
2. Precipitate – Metals become particles
3. Flocculate – Group particles together
4. Filter – Remove from system
5. Vacuum – Collect from bottom

Step by step:

1. Adjust pH to 7.2-7.4
2. Add shock chlorine (20-30g/m³)
3. Let water turn brown (normal)
4. Add flocculant (as per dose)
5. Turn off pump 8-12 hours
6. Vacuum bottom to waste (not to filter)
7. Repeat if necessary

Method 3: Pre-Filtration

For those who regularly fill with well water:

Equipment:

Install before the pool inlet.

Manganese Treatment

Symptoms of Manganese

• Dark brown or black water
• Black stains on liner or tiles
• More difficult to remove than iron
• May look like "sludge" on bottom

Treatment

Similar to iron, but more persistent:

1. Higher pH: Raise to 7.8-8.0 (manganese oxidises better)
2. Higher chlorine dose: 30-40g/m³
3. Flocculant: Double dose
4. Time: Let precipitate 12-24 hours
5. Vacuum to waste

Manganese is more stubborn than iron – may need 2-3 treatment cycles.

Hardness Treatment (Calcium)

Symptoms of Hard Water

• White/limescite deposits on surfaces
• Cloudy water that won't clear
• Scale on equipment
• White waterline
• Excessive chemical consumption

Hardness Levels

Treatment Options

1. Calcium sequestrant:

• Prevents scale formation
• Reapply monthly
• Doesn't remove calcium

2. Dilution:

• Mix well water with mains water
• 50/50 if hardness > 500 ppm
• Simple and effective solution

3. Acid (with care):

• Lowering pH reduces precipitation
• Maintain pH 7.2-7.4
• Monitor alkalinity

4. Partial water change:

• Replace 20-30% of water
• Repeat until acceptable levels

Filling the Pool with Well Water

Recommended Procedure

Before filling:

1. Analyse well water
2. Prepare necessary products:

• Metal sequestrant
• Granular chlorine
• Flocculant
• pH regulator

1. Clean well if necessary

During filling:

1. Add metal sequestrant while filling

• Dose: 30-50ml per m³
• Helps prevent oxidation

1. Don't add chlorine yet
2. Check well pump operation

After filling:

If Water Turns Brown

Don't panic – it's normal with iron-rich well water:

1. Don't add more chlorine (makes it worse)
2. Add flocculant as per dose
3. Turn off pump
4. Wait 8-12 hours (particles settle)
5. Vacuum bottom to waste
6. Refill what you vacuumed
7. Repeat if necessary
8. Add sequestrant before next chlorination

Ongoing Maintenance

Weekly Routine

Monthly Routine

• Complete water analysis
• Check equipment for scale
• Clean salt cell (if applicable)
• Extended filter backwash

When to Drain and Start Over

If the water has:

• TDS > 2500 ppm
• Irremovable accumulated metals
• Permanent stains formed
• Chemicals not working

It may be more economical to drain and start fresh with correct treatment.

Margem Sul Specific Issues

Areas with High Iron

• Moita (especially rural areas)
• Barreiro (industrial zones)
• Parts of Palmela
• Montijo (some areas)

Recommendation: Pre-filtration or mixing with mains water.

Areas with Hard Water

• Setúbal (limestone water)
• Azeitão
• Sesimbra (some areas)

Recommendation: Regular calcium sequestrant, strict pH control.

Areas with Brackish Water

• Alcochete (near river)
• Montijo (low-lying areas)
• Some coastal wells

Recommendation: Very high TDS – consider mixing or alternative source.

Cost Comparisons

Well Water vs. Mains Water

Well water can be more economical, but requires more work and knowledge.

Recommended Investments

Frequently Asked Questions

Can I fill the pool with only well water?

Yes, as long as you treat it properly. Ideally, analyse first and have products ready. If metal levels are very high (iron > 1 ppm), consider mixing with mains water.

Why does the water turn brown after adding chlorine?

Chlorine oxidises dissolved iron (invisible) transforming it into ferric iron (visible, brown). It's a normal chemical reaction. Treat with flocculant and vacuum to waste.

How much metal sequestrant should I use?

Typically 30-50ml per m³ for initial treatment, then 15-25ml per m³ weekly for maintenance. Always follow manufacturer instructions as it varies between products.

Can well water damage equipment?

Yes, especially if it's very acidic, very hard or with high metals. Iron can permanently stain liners. Hard water creates scale in pumps and heaters. Keep pH and chemicals balanced.

How long does iron treatment last?

Sequestrant treatment lasts 2-4 weeks. Removal by flocculation is permanent for that water, but when you add more well water, more iron enters. Pre-filtration is the most lasting solution.

Conclusion

Using well water for your pool is perfectly viable in Margem Sul, provided you take the correct precautions. The essential points are:

• Always analyse before filling – avoids surprises
• Use metal sequestrant – prevents staining
• Treat iron/manganese correctly – flocculant + vacuum to waste
• Control hardness – prevents scale
• Regular maintenance – add sequestrant weekly

If you need professional help with your pool in Margem Sul, ManutençãoPiscinas is here to help. Contact us for a no-obligation quote.