Reducing Non-Revenue Water

Reducing Non-Revenue Water
The benefits of reducing NRW include:
• need for less water to be produced, treated, and pumped, translating into the postponement of the expansion of capacity—producing less water also translates immediately into cost savings on O&M, due to savings in energy and treatment costs;
• reduction in apparent losses, which will result in more water being billed and more revenue for utilities—it has also been shown that water metering and adequate rates reduce wasteful consumption, which will likely decrease total consumption;
• adequate understanding of consumption patterns, which will allow utilities to optimize distribution systems;
• better knowledge of real consumption, which will improve demand projections; and
• reduced sewage flows and pollution.
These benefits depend on adequate pricing of water resources and services. Subsidies for water extraction, discharge of wastewater, capital investment, and operation of water supply systems lower
the cost of water as perceived by utilities and thus remove an incentive to reduce physical losses. Low water rates for consumers do not encourage utilities to meter their water consumption and detect and deter unauthorized water use. Moreover, low rates fail to provide consumers with an incentive to deal with leaks and wastage beyond their meters. It is often said that there is no point in reducing

NRW below about 20% of production, because the costs outweigh the benefits.

STEP TEST

Step test merupakan suatu metode yang diterapkan sebagai langkah penapisan (scoping) jaringan dalam upaya mempersempit wilayah/area aliran air untuk memperkirakan lokasi dan besarnya kebocoran air.

Step test dilakukan mulai dari wilayah terkecil yakni sub zona. Step test diperlukan untuk menentukan prioritas pengawasan jaringan terhadap kebocoran.

            Prinsip step test adalah sebagai berikut ;

1. Penutupan valve secara bertahap mulai dari valve terjauh secara berurutan menuju valve yang terdekat dengan distrik meter.
2. Bagian demi bagian semakin tertutup terhadap water meter sehingga aliran air menjadi nol.
3. Kemudian bagian demi bagian dibuka kembali mulai dari valve terdekat dengan distrik meter hingga valve terjauh, sebagai faktor pembanding debit pada tahap penutupan.
4. Perubahan (selisih) dan aliran air (Q) air tiap tahapan merupakan indikator adanya kebocoran secara KUALITATIF.

MANAJEMEN TEKANAN

Tekanan berhubungan dengan kebocoran, semakin tinggi tekanan, semakin tinggi kebocoran. Menurunkan tekanan berdampak langsung dengan penurunan kebocoran. Pengelolaan tekanan merupakan salah satu cara penurunan kebocoran yang paling murah dan efektif. Pengelolaan tekanan bisa mengurangi frekuensi pipa pecah, karena fluktuasi tekanan yang ektrim, dan bisa memperpanjang umur pipa.

Tingkat kehilangan air berubah-ubah sesuai dengan perubahan tekanan. Secara sederhana kebocoran pipa merupakan aliran dari dalam pipa melalui lubang kecil, yang rumus umumnya adalah;

Q = Cd x A x V                              …… a

Apabila, V =  (2gh)^0.5 , maka;

Q = Cd x A x (2gh)^0.5                           …….. b

dimana:

Q    = volume air yang keluar (m³/dt)

A    = luas lubang (m²)

V    = kecepatan (m/dt)

Cd = koefisien kontraksi

g    = gravitasi

h    = tekanan (m)

               Memahami hubungan tekanan dan kebocoran dalam sistem jaringan distribusi merupakan kunci untuk mengendalikan tingkat kehilangan air. Dengan mengurangi tekanan, secara signifikan volume kebocoran air bisa diturunkan Hubungan tekanan dan kebocoran dalam sistem jaringan pipa sangat kompleks. Bentuk lubang yang tidak teratur, pola-pola lubang yang bermacam-macam. Bentuk dan ukuran lubang mengikuti material pipa, tekanan dan gaya-gaya eksternal yang bekerja pada pipa.

            Tekanan maximum dan variasi tekanan (untuk jam pelayanan “intermittent”), sangat erat hubungannya dengan pipa pecah, oleh karena itu, menstabilkan tekanan atau pengendalian tekanan sangat penting dalam sistem dengan tekanan rendah.  

WATER BALANCE

Standard Water Balance

The major challenge facing water utilities and municipalities

is how to deal with high levels of Non-Revenue Water (NRW).

NRW is the gap between the amount of water put into the

distribution system and the amount of water for which

customers are actually billed.

High levels of NRW reflect huge volumes of water being

lost through leaks (real/physical losses), water not being

invoiced or not being accurately measured (apparent/

commercial losses) or both.

A water balance audit details how much of each type of loss

is occurring and how much it is costing the water utility. The

key concept behind this approach is that water should not

be “unaccounted-for”.

In conducting a water balance audit, a quantity is determined

for the major components of water consumption and water

loss, and a price is placed on each component in order to

assess its financial impact on the water utility. A detailed and

accurate water balance forms the basis for an effective NRW

management strategy.

WATER BALANCE

International Water Association Water Balance

The following are definitions of principal components of IWA water balance.
• System Input Volume is the annual volume put into the part of a water supply system that relates to
water balance calculation.
• Authorized Consumption is the annual volume of metered and/or non-metered water taken by
registered customers, water suppliers, and others who are implicitly or explicitly authorized to do so
for residential, commercial, and industrial purposes. It includes water that is exported.
• Water Losses can be identified by calculating the difference between system input volume and
authorized consumption. They consist of apparent losses and real losses.
• Apparent Losses result from unauthorized consumption and all types of inaccuracies associated
with metering.
• Real Losses result from losses at mains, service reservoirs, and service connections (up to the
point of customer metering). The annual volume lost through all types of leaks, bursts, and overflows
depends on their individual frequencies, flow rates, and duration.
• Non-Revenue Water is the difference between system input volume and billed authorized
consumption, and it consists of the following:
• Unbilled Authorized Consumption (usually a minor component of water balance),
• Apparent Losses, and
• Real Losses.