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Did you know that about 20% of energy in California is used to pump or treat water as compared to the 4% nationwide? That is a huge portion of the state’s total energy use. The reason for this is in California we have to move large quantities  of water from a source to the final point of use. Water from the Bay delta is moved 400 miles to San Diego. It has be pumped over two mountains ranges along the way.

The term water energy intensity captures the amount of energy that is used to make/deliver water. For instance, in East Bay MUD water energy intensity is 1.25 MWH per Million Gallons of water (based on 2006 numbers). EBMUD needs to pump water up the Oakland and Berkeley hills and that accounts for a significant portion of the energy use in their water.

The relationship between water and energy has been known and studied for a while (e.g., see the pioneering work of Professor Wilkinson’s on the energy intensity of water), but this information still appears to be largely ignored. There are few if any real bridges between the water and energy industry or professional silos. To better manage energy, you need to understand how the biggest customer, water agencies, are using the energy.

There are four main energy uses in a typical water system:

• Pumps to extract ground water and to deliver water from source to a final point of use.
• Water treatment and distribution with in a service area.
• On-site water pumping, treatment and thermal inputs (heating and cooling).
• Waste water collection and treatment.

EPA offers a top 10 list of ways to manage water. The best way to manage water is to Meter, Measure, and Monitor the water use for each building or facility. This information can help detect leaks and the knowledge of water usage will lead to greater water efficiency.

In commercial buildings, the main user of water & energy are cooling towers. Some use as much as 30K gallons of water per day. Metering the quantity of water put into and discharged from the cooling tower provides information that helps better manage the efficiency of the cooling tower.

Irrigation often accounts for 50% of a facility’s total water use. So minimizing the water used for irrigation will have a significant impact to the overall amount of water used.

According to the Energy Independence and Security Act of 2007, all Federal buildings are required to measure and verify energy and water usage and savings. The list of Best Management Practices is well worth reading.

Per capita water use is calculated by dividing the total amount of water withdrawn from all water suppliers by the population. Water used for irrigation and agriculture is not included. See this excellent summary report on per capita use in Florida.

The Water Resource division of the U.S. Geological Survey (USGS) publishes the Estimated Use of Water in the United States every five years. This report has detailed per capita water usage on a state by state and county by county level.

In California, Kern county has the highest per capita use of water at 274 Gallons per Day, & Mariposa has the lowest at 67 GPD. Santa Clara is 171 GPD and San Diego county is 156 GPD. Sacramento & Fresno don’t have a lot of meters and consequently they use more water at 265 GPD and 246 GPD, respectively.

Interesting lecture on the laws of water use in USA by Prof. Glennon given at the UC Berkeley California Colloquium on Water. Some of the facts cited in this talk:

• Groundwater use for domestic purposes alone 8 BGD (Billion Gallons per Day) in 1965 to 19.7 BGD in 2000.
• Farmers use 2/3 of all groundwater pumped.
• Total groundwater use in 2000: 30 trillion gallons
• Groundwater makes up 25% of the nation’s water supply
• 1/2 population relies on groundwater for drinking water

But these numbers are quite out of date. During the past decade people have turned to groundwater to supplement the short supply of water caused by draughts. This means that much more water must have been pumped from new and existing groundwater sources than in 2000 (the last year for which there is data from the US Geological survey).

Surface water law. If you own property on a lake or river, then you’ve water rights. This is called the Riparian Water Rights (which has its origin in English common law). It is a shared water rights (all land owners that are on the river or lake share the water rights). In the western USA, a different law is in place: Prior Appropriation. In this system, water rights are unconnected to land ownership. The first person to use a quantity of water for a beneficial use (agricultural, industrial or household use), has the right to use that quantity of water for that purpose. Each water right has a yearly quantity and an appropriation date.

Groundwater law: Rights of Capture & Reasonable Use. The problem with the groundwater law capture and reasonable use is that it allows for over-drafting or mining the resource to the extend of exhausting the supply. Basically anything you can with groundwater is considered reasonable.

These are the basic laws for water. One set of rules for surface water and one set for groundwater. Think of a ground water as a glass of water and each groundwater user having a straw. The groundwater laws allows for unlimited supply of straws. This leads to exploitation of groundwater aquifers.

Water is measured in acre-foot. That is how much water it takes to cover an acre of land to the depth of one foot with water. An acre water is 325,000 gallons, and weights 1358 tons. So water is really heavy and it takes a lot of energy to pump it out of the aquifers. Pumping water out of a 500 feet well will require many kilo watts of energy (multi $K per month).

Problems with over-drafting:

• The water quality is lower the deeper the well.
• Salt-water intrusion.
• Subsidence. The land collapse when groundwater is pumped too quickly without giving the aquifers times to naturally replenish (rate of 2 inches per year).

Groundwater moves laterally and it actually provides water to the rivers.

I’ve had the Rennai tankless hot water system for four years now [manual, spec, warranty]. Overall I’m happy with not having a hot water tank in the house, but in some faucets the hot water is not consistent. For example, in the kitchen, where you need a reliable constant hot water, the Rennai is kind of disappointing. It does eventually get hot, but then sometimes it may turn luke warm. 

The kid’s shower and faucet are, however, extremely reliable. As soon as they turn the hot water on, they get constant hot water.

In the master bedroom, the shower/faucet does get hot, but it takes over a minute and then it turns cold, before it turns hot again. A trick that I’ve learned is to turn off the hot water at the first sign of turning cold, wait for a few seconds, and then turn it on again. This seems to work, i.e., get the hot water flowing quickly after that. Renni 

So why the inconsistencies? The house water pipes may have something to do with this. The recirculating pump may also be an issue. The Rennai system does warn about the interactions of a recirculating pump and the tankless water system. But given the pipe layout of our house, a recirculating pump is needed otherwise some faucets may take a long time to deliver hot water.

Every time we have an power outage, the temperature gets set at 110 degrees Fahrenheit. This external temperature control allows me to set it back to the maximum setting of 120 degrees. There is another external module that allows you to set the maximum temperature of 140 degrees. I should’ve ordered that module.

The Gundfos system now has specific recirculating pumps for tankless water systems. In addition to the recirculating pump, I also added the external temprature control. With a recirculating pump, there is low flow in the pipes all the time, this causes the tankless water system to run constantly. To avoid this, I also added the Grudfos’s timer and temperature control. With the timer, I turn off the recirculating pump at night, and the temperature control turns off the pump if the temperature of the pipe is already hot.

I have the outdoor version of the Rinnai tankless water heater. It requires a gas line, water line and electricity. As far as capacity, we have ran multiple appliances, taken a shower, etc, without a hot water issue.

A typical residential water service in our area has a dynamic water pressure of about 65 PSI, and a 3/4 or 1 inch supply line. This roughly translates to about 17 to 32 gallons per minute maximum water flow.

Well exactly how much water is that?

32 gallon = 512 cups = 4096 ounces = 24576 teaspoons

17 gallon = 272 cups = 2172 ounces = 13056 teaspoons

32 gallons per minute is the same as 512 cups per minute, 4096 ounces per minute, or 24576 teaspoons per minute. Which is 0.53 gallons per second, 8.533 cups per second, 68.26 ounces per second or 409.6 teaspoons per second.

17 gallons per minute is 0.2833 gallons per second, 4.533 cups per second, 36.2 ounces per second or 217.6 teaspoons per second.

I’ve a 3/4 inch supply line with 65 PSI dynamic water pressure and I was expecting the maximum of 17 gallons per minute. Based on my actual measurement, I was able to get about 12 gallons per minute.

I took three measurements from the closest water outlet to the water meter, and on average I was able to get 1 gallons per 5 seconds (12 gallons per minute or 3.2 cups per second). I’m sure that just after the meter, the rate will be closer to 4.5 cups per second. I also took a measurement at the water outlet furtherest away from the meter but still with minimum splits and turns, and as expected I was getting a lower flow rate — 1 gallon per 7 seconds.

Static Water Pressure is the water pressure measured as close to the water meter by hooking up a pressure gauge to the pipe before the meter.
Dynamic Water Pressure is the pressure that you’re left with after the water flows thru the meter, the back-flow device, and all of the pipes.


1 CCF = 748 gallons
1 gallon = 16 cups
1 cup = 8 ounces
1 ounce = 6 teaspoons

1 pint = 2 cups
1 quart = 2 pints
1 quart = 4 cups
1 gallon = 4 quarts


Here is how you can calculate the water flow rate

Q = V * A

where, Q is the Volumetric flow rate, V is the velocity of the water, and A is the cross-sectional area of the passage.

You can compute the velocity of the water

P0 - P = (rho) * V ^ 2

Where P0 is the total pressure calculated using a pitot-static tube, P is the static pressure, rho is the density of the fluid (water has a density of 1), and V is the Velocity of the water.

Most Water Utilities in North America and Britain charge water per CCFs (748 gallons per CCF). In our area a CCF is about $2.25.

1 gallon = 0.3 cents
1 cup = 0.0019 cents
1 toilet flush = 1.6 gallon = 0.48 cents