The Department of Statistics keep tabs on everything, including water and every five years they put out a fairly comprehensive report on how much comes down, some figures on how much gets abstracted and how much stored and how much flows to sea.

Apparently New Zealand gets about 600 billion cubic metres of rainfall each year, although some regions get a lot more than their fair share and others less so. Some years we all get more and in others more than half a billion less.

In the realms of abstraction, statistics get a bit short on actual figures because there simply aren't enough water meters around the place to get reliably statistical measurements.

But there is a whole section on livestock drinking water and dairy shed requirements, which provide some food for thought.

The Resource Management Act has stock drinking water as a permitted activity and in the year to June 2010, New Zealand's dairy cows were estimated to drink 113.3 million m3. The estimate for dairy shed water (washing equipment and the shed area) was 84.9 million m3.

The latter did not include an allowance for yard washing. To give an idea of how much that looks like, it's an equivalent of 198 Olympic-sized swimming pools of water every day for the year.

Since 1995, the estimated national water usage for these two activities has increased by 49.2 million m3, of which an extra 28.4 million m3 was presumably drunk and 20.8 million m3 extra got used for washing dairy sheds – the number of which have grown hugely in that time.

To give a local perspective, between 1995 and 2010, cow numbers increased by; 195,961 – 17.4 per cent in the Waikato; and 46,467 – 16.3 per cent in the Bay of Plenty.

Those extra cows, at 70 litres per day each, drink an extra 17 million litres or 17,000 m3. The total herds in these two regions – 1,656,560 cows – now guzzle down 20 million m3 a year and we haven't begun to wash sheds yet. No wonder dairy farmers' power bills are going up.

This isn't a diatribe on using less water. Rather, it's a wake up call for farmers to use what water they have to as sensibly as possible, even if only to save power on running pumps needlessly.

There are rules on using only clean water to wash sheds and plant. Yards don't have to be cleaned with clean water. Recycling cooling water and maybe plant washdown water and catching shed roof water makes good sense. Putting it all through a tank and then using it to wash the yards not only saves water, but reduces the amount going into the effluent storage.

Why build a storage ‘lake' when you could get away with a much smaller ‘pond'?

Installing water meters may seem an expense you could do without, but with the new regulations being introduced by regional councils – particularly after the change last year to the Resource Management (Measurement and Reporting of Water Takes) regulations which requires meters for any industrial take over five litres per second –they are probably going to be something farmers have to do anyway.

A number of those who tried water meters early in the piece have done some hard thinking about their actual water usage and found ways to save money by using it better. Not to mention finding pipe leaks before they've produced new wetlands on the farm.

So next time you find yourself standing in the yard at the end of milking, dreamily squirting that huge hose around or discover your worker doing it – ask yourself if it's delivering more than five litres a second.