How to Prevent Tank Algae in a Campervan

Green water, slimy pipes, and a musty smell means algae in your fresh water tank. Here is how to prevent it and what to do when it appears.

Summary

Opaque tank + Puriclean + drain between trips = no algae. Takes 5 minutes per fill-up and saves you a grim afternoon scrubbing a slimy tank.

Why Algae Grows

Algae needs three things: light, warmth, and nutrients. Your water tank provides all three if you:

• Have a translucent or white tank (light gets through)
• Keep the van stationary in warm weather
• Leave water sitting for more than 2-3 weeks
• Fill up from questionable sources

Prevention

• Use an opaque tank. If your tank is translucent, paint it with black or grey plastic paint (PlastiKote, £6 per can). Light exclusion is the single best prevention.
• Keep it cool. Mount the tank inside the van (under a seat or in a cupboard), not in an external locker exposed to direct sun.
• Use a tank additive. Puriclean (tablets, £8 for 20), Aqua-Safe, or Milton tablets (sterilising, £4 for 32) added every time you fill up. Follow the dosage — too much leaves a taste.
• Sanitise every 3 months. 50ml of thin bleach in a full tank, drive 20 minutes to slosh it around, leave 4 hours, drain, flush twice with clean water.
• Drain between trips. If the van sits for more than 2 weeks, drain the tank. Standing water is an algae invitation.

Treatment

Already green? The full clean:

1. Drain the tank completely.
2. Remove the tank if possible for a thorough scrub.
3. Fill with water + 100ml thin bleach per 20 litres. Leave 6 hours.
4. Drain and flush 3 times.
5. Refill with water + Puriclean or Aqua-Safe.
6. Run the pump and open all taps until the solution comes through. Leave 30 minutes.
7. Drain and flush again.
8. Repeat steps 5-7 with clean water only (no additive) to remove bleach taste.

Pipe Maintenance

Algae also grows in pipes. After treating the tank:

• Disconnect the pipes where possible and soak in bleach solution
• Replace flexible hose if it is more than 2 years old (£3 per metre, B&Q)
• Fit a clear sediment filter (£15) between the tank and pump

Filling Up

Avoid filling from: rivers, untreated standpipes on farms, old hoses left on the ground. Use: campsite mains water points, dedicated drinking water taps, your own hose (food-grade, never used for anything else).

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