This guide explains how to collect roof rainwater, store it so it stays clean, and filter it to the right standard for the job — whether that is irrigation or drinking water for livestock. The two uses demand very different levels of treatment, and understanding that difference is the key to doing this safely.

Why roof water is not "clean" water

It is tempting to assume rainwater is pure. The rain itself is reasonably clean, but the moment it lands on a roof it stops being so.

As water runs across the roof it picks up dust, pollen, leaf litter, moss, and — most importantly — bird and animal droppings.

Droppings are the main reason roof water can carry harmful bacteria such as E. coli, along with other organisms that cause disease in animals.

Roof water can also pick up substances that leach from the roof itself, from flashings, or from gutters.

This matters a great deal for livestock, and it is why the choice of roofing and guttering material is not a detail to overlook.

The roof: your collection surface

How much water can you collect? The maths is straightforward. One millimetre of rain falling on one square metre of roof yields one litre of water.

Roofing and guttering materials matter. Some materials are well suited to water collection; others can contaminate the water, and a few pose a specific danger to certain animals.

Generally suitable surfaces include coated steel sheeting, factory-coated aluminium, clay and concrete tiles, slate, and EPDM rubber membranes — these are stable and shed water cleanly.

Materials to treat with caution or avoid

• Copper roofing, flashing or pipework leaches into water and is highly toxic to sheep in particular.
• Lead flashings and old lead-based paints can leach lead, which is harmful to all livestock.
• Bitumen and tar-coated roofs can leach compounds into runoff and are best kept for irrigation-only collection.
• Asbestos cement sheeting, common on older roofs, is a handling and health hazard — never cut or disturb it without specialist contractors, and don't drink water from it without professional advice.
• Moss-covered or overhung roofs shed organic matter and droppings; keep roofs clear and trim back branches.
  
  

Sheep & copper

Keeping debris out before it reaches the tank

Good water quality begins at the gutter, not the filter.

The aim is to stop as much dirt as possible from ever entering the tank, because whatever gets in has to be dealt with later.

Gutter guards and leaf screens fitted along gutters and over downpipe inlets catch leaves, twigs and larger debris. Mesh screens over the tank inlet form a second barrier and keep out insects, rodents and birds.

A first-flush diverter is one of the most valuable and inexpensive components in the whole system.

When rain begins, the first water off the roof carries the highest concentration of droppings, dust and grime accumulated since the last shower.

A first-flush device diverts this initial dirty water away from the tank — typically the first half a millimetre or so of rainfall — before allowing the cleaner water that follows into storage.

The diverted water drains slowly away through a small outlet, resetting the device ready for the next downpour.

Storing the water so it stays clean

Storage is not just a matter of holding water — a well-designed tank actively keeps water clean, while a poor one lets it spoil.

Choosing a tank. Common options are polyethylene (HDPE), concrete, glass-reinforced plastic (GRP), and coated steel. For irrigation, almost any watertight, non-toxic tank will do.

For drinking water, use a tank certified as food-grade or potable-water safe — the manufacturer will state this — and avoid any tank, liner or fitting not rated for potable use.

(Note: We are a water filter company and can offer you various water treatment options. You'd probably be assembling a system that might also include tanks and pumps. We don't supply those at this time. But they are readily available from good specialist suppliers. Contact us for recommendations)

Keep it dark, covered and cool

Three simple principles prevent most storage problems:

• Dark stops sunlight reaching the water, which prevents algae. Use an opaque tank or shade it.
• Covered and sealed keeps out leaves, insects, vermin and birds, and stops mosquitoes breeding. Screen the vents and overflow.
• Cool slows bacterial growth. Underground or shaded tanks stay cleaner than a black tank baking in the sun.

Design the internals to your advantage

A calmed inlet directs incoming water gently rather than splashing it in, so settled sediment isn't stirred up.

Heavier particles then settle to the bottom, leaving cleaner water above.

Drawing from a floating take-off that sits just below the surface — rather than from the bottom where sediment collects — means you always draw the cleanest available water.

The overflow should be screened, and ideally skims floating debris off the surface when the tank overflows.

Sizing the tank means balancing three things: how much your roof yields, how much you use, and how long your dry periods last. It is often more economical to have a large collection tank feeding a smaller, treated day-tank than to treat an enormous volume all at once.

Matching the standard to the use

This is where irrigation and drinking water part ways. Both benefit from removing dirt; only drinking water needs the full water filtration approach that removes disease-causing organisms as well.

Understanding livestock water quality standards

Before relying on harvested water for stock, and periodically thereafter, have it tested by an accredited laboratory. A vet or your testing lab can advise on the right suite of tests. As a general guide, the parameters that matter most for roof-harvested water are:

• Bacteria (total coliforms and E. coli) — the single most important test, because the main risk is faecal contamination from birds and animals. For drinking water, E. coli should ideally not be detectable.
  
  
• pH — most livestock do well in roughly the 6.0–8.5 range. Rainwater is naturally slightly acidic, which is rarely a problem but worth confirming.
  
  
• Total dissolved solids (TDS) — here roof rainwater has a natural advantage: it is very low in TDS, making it excellent drinking water once the microbial risk is dealt with.
  
  
• Contaminants from roofing — such as lead, zinc or copper, particularly if any part of your system uses the materials flagged above.

Different species, ages and production stages have different tolerances — lactating and young animals are the most sensitive — so treat published figures as starting points and lean on your vet and lab for decisions specific to your stock.

Maintenance keeps the system safe

A rainwater system is only as good as its upkeep. A neglected one can quietly deteriorate until the water does more harm than good. Build a simple routine:

• Regularly clear gutters, leaf screens and inlet meshes, and check the first-flush diverter is draining and resetting.
• Every few months, inspect the tank for sediment, and check lids, seals and screens remain intact and vermin-proof.
• Replace or clean filter cartridges on the manufacturer's schedule, or sooner if flow drops off.
• For UV systems, replace the lamp roughly annually and clean the quartz sleeve so light reaches the water.
• Test the water quality at least annually for drinking systems, and after any fault or health concern — more often in the first year.
• Keep the roof clear of moss and overhanging vegetation, and check flashings and coatings for damage.
  

Responsibilities

A note on rules and responsibilities

Regulations around rainwater use vary by country and region, and they change over time, so check the current position with your local authority, environmental regulator and any farm assurance scheme you belong to before you commit.

In general, harvesting rainwater from your own roofs for irrigation and yard use is widely permitted with few restrictions.

Using harvested water as drinking water for livestock, or for irrigating food crops, brings additional responsibilities: many farm assurance schemes require a documented risk assessment and regular water testing to demonstrate the water is fit for purpose. If your farm belongs to such a scheme, confirm their requirements at the design stage rather than after installation.

Three things to get right

Get those three right, and a resource that once ran off your roof into the drain becomes one of the most dependable and cost-effective water supplies on the farm.

How we can help you: we stock a wide range of good value Ultra Violet filters plus sediment / pre-filters and other filtration methods that can help you turn your rainwater into potable water for irrigation and livestock drinking water. Contact us to discuss your agricultural rainwater harvesting requirements.