Water systems – what do you need to know?

It’s in warm dry weather like last week and this week when a water system on a livestock farm, dairy and suckler in particular, comes under pressure. Pat Tuohy from Teagasc Moorepark co-ordinated a demonstration at the Moorepark Open Day this week and water was a key part. Here we take a look at the water issues.

Common problems on most farms can usually be: the water source (well, mains or river), the pumping equipment, pipe sizes, ballcocks and water troughs.

Concrete water troughs are the preference now for most farmers – if they empty out, the stock won’t be able to push them all over the field. The water troughs need to satisfy two main criteria – water volume and drinking space. Researcher Pat said: “The volume of the trough needs to allow for storage of 5-7 litres/cow, while 45cm (18in) of drinking space along the trough rim is required per cow. It is advisable that 10% of the herd can drink at the same time as cows tend to act like a herd and drink at similar times and bully cows can sometimes take up a lot of space at a water trough”.

The message at the open day was carefully consider trough location. In the past, some farms have put water troughs at gateways or halfway down a farm road etc, but that is the wrong place to put a water trough. Cows don’t like to walk more than about 250m to get a drink. When positioning troughs, allow for ease of splitting paddocks with temporary fences, and to allow as much access as possible, making sure they are not too close to fences or boundaries. Multiple troughs may be needed in many cases to ensure good supply, location and access, particularly in heavy ground where potential for poaching needs to be minimised.

Farmers, especially expanding dairy farmers, need to calculate what volume of water is required. Volume required is not spread evenly throughout the day but tends to be concentrated in a period before and after milking.

Flow rate must be capable of supplying this peak in demand. Pat said: “If we assume a daily demand of 80 litres/cow and that half this volume needs to be consumed in a three-hour period, then a flow rate of 13 litres/cow/hour is required (ie 80 x 50%/3 = 13 litres/cow/hour).

Pat then explained how to check the water flow rate in a trough.

1 Mark the level of water in a trough.

2 Tie up the ballcock and empty, say, 25 litres from the trough.

3 Release the ballcock, hold it down and measure the time it takes (in minutes) to refill to the original mark.

4 Divide the 25 litres by the time taken to refill, eg if it takes a minute to refill then the flow rate is 25 litres/minute (25/1 = 25).

5 If the flow rate measured is less than that required for your herd, then your water supply system needs to be improved. Check the flow rate of troughs around the farm.

At the open day, farmers heard there are a number of factors which will dictate the flow rate of water to each trough, namely:

Obviously, an adequate source of water is fundamental to the supply, and if this isn’t capable of supplying the needs for drinking (as well as that required for other purposes, mainly milking plant/parlour washing and domestic needs), then efforts will need to be directed at improving supply whether from a private well, public water source or local scheme. Where source water is limited, reservoirs and pumps can be utilised to buffer against shortages during periods of peak demand.

The size, length and layout of the pipe network will dictate the pressure achieved at the ballcock and the flow rate from there is dictated by the valve and jet size in the ballcock. Water pressure available at source will be reduced by travelling through the pipe network. The amount of pressure loss will depend on pipe length and diameter. The reason the flow rate reduces is because of friction between the water and the inside surface of the pipe.

When using 0.5in (12.5mm) pipes, which is common on many farms, flow rates would be very small as the pressure loss would be very high ie only a trickle coming out. Pat said: “Always bear in mind that a 20 mm (0.75in) pipe has approximately twice the crosssectional area of 12.5mm (0.5in) pipe. Similarly, a 25mm (1in) pipe has four times the cross-sectional area of 12.5 mm (0.5in) pipe, although it’s only twice the bore.”

Very often the ballcocks are the weak link in an otherwise satisfactory water supply system. Ballcocks are frequently over-restrictive, even on systems where the pipe sizes are adequate. A high-pressure 12.5mm ballcock in the drinking trough is not capable of allowing an adequate flow rate, which is in most situations about 16 to 22 litres /minute (3.5 to 5gal/min). In general, standard ballcocks are described by their size and pressure. Ballcocks can have high, medium or low pressure jets.