Two major factors will dictate if the current water system in place is fit for purpose or if modifications are required - trough size and flow rate of pipes.

Peak demand for water occurs at peak grazing time, which, for dairy herds, is after each milking.

Teagasc suggests that up to 50% of the daily water intake of a cow occurs in the three hours after each milking.

It is recommended that 10% of the herd is able to drink at the one time, with each cow requiring 450mm of trough space.

Typically, rectangular troughs have a greater perimeter water capacity ratio compared with round or elliptical troughs.

Recommendation

A recommendation by Teagasc is for a trough capacity of nine litres/two gallons per cow, equating to a 900-litre or 300-gallon trough for a 150-cow herd.

Cows should never be more than 250m from a trough to encourage drinking, with troughs placed in the centre of paddocks for this reason and to encourage even graze-outs. Troughs should be situated on an elevated, dry site.

Pipe diameter

A far more common issue with water supply on farms is inadequate pipe diameter resulting in poor flow capacity.

As herd sizes have increased, so too have milking platforms and the distance water must be piped.

The further the distance water has to travel through a pipe, the greater the loss of pressure due to friction between the water and the internal pipe surface.

Water piping should be a minimum 25mm in diameter, rising to 40mm for larger herd sizes. / Donal O'Leary

For example, at a flow rate of 3m3 per hour (50l/min or 11gal/min) with a 32mm (1¼ inch) pipe, the pressure is reduced by 4.83psi for every 100 metres of pipe.

To determine flow rate in a trough, lift the ball cock, empty a fixed amount (eg 50 litres) and time how long it takes the trough to refill. A simple calculation will ascertain the litres/minute flow rate.

Where flow rate is inadequate, a larger-diameter pipe can be installed.

For herds of less than 150 cows, pipe diameter should be a minimum 25mm (1in) and for herds of 150 to 300 cows, this should rise to 32mm minimum (1.25in). A 40mm (1.5in) pipe should be installed for herds greater than 300 cows.