Sep 17, 2011

Demand Forecasting for Dhaka City

Dhaka is a huge city. It has a large number of population. Water is the basic need. At present 75% city area is under Dhaka Water Supply & Sewerage Authority (DWASA) water supply coverage, out of which 82% is from groundwater sources tapping through 411 Deep Tubewells (DTW); the remaining 18% of the water is supplied from the two major water treatment plants situated at Saidabad, Chadnighat and two smaller units in Narayanganj. The population of Dhaka city, Narayanganj and Tongi is presently more than 10 million and the growth trend indicates that by the year 2010 it would be about 13.4 million. The increase of population would create further water supply demand of additional 120% of present production, which has to be met either from the surface water sources or by sinking additional DTW. 

In order to meet the growing demand, DWASA is installing high capacity water wells tapping the upper aquifers. But this upper aquifer is in stressed condition. In most part of the city area the groundwater recharge in upper aquifer is much less compared to the abstraction, causing groundwater mining. The average groundwater depletion in most of the areas in the city is reportedly around 2-3 m/year. The present rate of depletion is alarming and may cause devastating events like land subsidence and other environmental degradation. This gives an alarming indication that there is an urgent need to alleviate pressure on the upper aquifer being exploited and explore for more suitable and sustainable sources to supplement the present water supply. 

The nearest dependable source of surface water is the Buriganga and Sitalakhya River. These rivers are no more considered to be suitable as a source of water supply due to continued pollution. For this reason, there is an urgent need to find alternate sources for Dhaka city water supply. Such probable source may include: exploiting the deeper aquifer (>300m depth) and surface water sources from far-off major rivers like Padma, Meghna and Jamuna. It is also worthwhile to investigate exploitable potential of aquifers located in the vicinity of Dhaka city. 

Demand management is another aspect, which has to be given utmost importance in order to optimise the use of the scarce water resources. Overall investigation, as mentioned, would support in the development of an immediate, mid-term and long-term strategy for water supply in Dhaka city. In this regard, prediction of the growing population along with the urbanization process, the various uses of water including domestic, commercial and industrial consumptions has to be evaluated. This study in essence has been formulated by DWASA aiming at developing a comprehensive water abstraction strategy for Dhaka city for the next 25 years. 

Current population of Dhaka City is 8.31 million, the total demand is 1606 MLD and it will rise up to 4073 MLD by the year 2030, an approximate rise by 2.5 times. This is based on no changes in the per capita demand for water except for the people living in katcha houses, where it has been assumed that a moderate rise of per capita water demand will increase from the current 53 liter to 100 liter. This change was made based on the assumption that the government of Bangladesh strive for achieving its MDG goals, water demand will increase at the poorest household for hygiene and for sanitary reasons.

To understand the impact on demand for water when various measures are adopted to alter both the demand and supply sides, five alternative cases were developed for the simulation exercise. These cases are expected to reflect changes that might happen in future. These are: 

Case I: Improvement in leakages from 30% to 20% 
Currently the physical leakage in the water distribution system stands between 30-40 percent. There is no accurate data on this. However, it has been stipulated that with improved management of the pipelines and their maintenance it can be reduced to 20%. Based on this assertion by experts, the model developed a case to understand the changes in the demand for water. 

Case II: Vertical rise in the height of multi-storey and hi-rise buildings
As the government has approved the new Dhaka Building Codes, it is expected the average height of Dhaka city will go up. Although it is difficult to assume how high the city will grow over the next 25 years, for the purpose of simulation it has been assumed that multi-storey buildings will increase its height to accommodate 10 families per unit instead of current 6 families per unit (already many buildings with 6 floors have increased its height by 2 additional floors in many parts of Dhaka city). Our survey data shows that with the current height hi-rise buildings accommodate nearly 27 families per unit while it could go up to 40 families per unit through raising the height of the building. The model assumed that the height will increase to meet this situation in the next 25 years. Based on these assumptions, demand for water has been estimated for the next 25 years using the model. 

Case III: Improvement in System loss plus Vertical rise of the city buildings 
Case III is designed to understand the cumulative impact on the demand for water if city height increases while at the same time there is improvement in the physical loss of water during distribution (possible through increased investment in water infrastructure and better maintenance). 

Case IV: Demand Management 
Survey data reveals a wide degree of variation in consumption of water per person per day for various types of houses. Table 3.1 shows that water consumption increases from 53 liter per person per day to as high as 238 liter per day per person for people living in hi-rise buildings. Interestingly, average per capita water demand is 124 while it is nearly 100 liters for people living is semi-pucca houses and around 140 for one-storey and multi-storey buildings. Considering, the huge variation in water consumption by differences in living standards, it has been assumed that it is possible to reduce water consumption to 140 liter per day if use of water-guzzling gadgets could be regulated in these buildings. The case IV presents the forecasts in demand for water if such measures are adopted. 

Case V: Improvement in system loss plus vertical rise in heights of houses plus demand management 
While the cases above are interesting, the survey data and also discussions around suggest that a more realistic future is when DWASA improves its efficiency in terms of controlling physical leakages, while at the same time the city goes higher in altitude and also a more stricter regulatory control is imposed on water-guzzling devices used at homes. This might be useful to reduce water demand to some tolerable limits from supplier’s point of view. Case V is designed to understand of such policy implementation. 

Based on the above cases, the baseline scenario is simulated using the model to forecast the next 25 years demand for water within DWASA territory. According to the model, if the Dhaka city develops as it is and no plan no demand management is established, the total water demand per day will increase from the current 1606 MLD to as high as 4629 (Case II) MLD. However, Case V suggests that with proper management of both water demand and water supply systems, it is possible to reduce the demand to 3780 MLD. However, it is also clear from the model that per capita water demand per day in liters will also increase from the current 123 lcd to 151 lcd if no demand management is imposed over the next 25 years. If, however, demand management and also supply efficiency are ensured it will come down to 141 lcd under the current baseline scenario.

Assuming that demand management is in place either through restricting sales of water-guzzling gadgets (for example by limiting the size of shanks, the number of bathrooms, improving the water taps, etc.) or by imposing a multi-layer tariff structure or both it is possible to limit the growth of water demand up to certain level. 

Implementation of demand management policies using 
i) Setting standards for water-related gadgets and banning of water-guzzling gadgets in Dhaka city. This is an important first step and it has been used in many other countries. It has been used by the Department of Environment to protect our environment. Under the Environmental Regulation standards have been set. Following this example, WASA should consider designing standards for: a) taps, b) shanks, c) roof top reservoirs, etc. 

ii) Changing differential pricing using multiple-tier– DWASA should consider institutionalizing a pricing mechanism that would be able to track both standard of living and also quantity of consumption. DWASA should consider improving the water supply system and at the same time charge differential tariff for two types of consumers– one basic tariff structure for people living multi-storey and hi-rise buildings and one basic tariff structure for people living in other houses. Secondly, there shall be multiple slabs in designing the tariff structure under each category. 

iii) Raising level of awareness about the waste of water among the consumers – many consumers are not simply aware of the water they often misuse because of carelessness. For example, shaving without shutting the tap wastes three times more water than with shutting. A standard toilet-flash wastes 20 liters of water while it can be done with less than 2 liters of water if improved gadgets are used. 

Development of a pricing policy to affect water demand needs further study. This sample is based on only 639 household and that the consumption of water is measured using actual payment data per household. The estimates is still within the range that has been used in similar other studies. However, it is possible to significantly improve the estimate if an elaborate study is taken using accurate physical measurement of water used per household from all over the Dhaka city. It could also be useful if DWASA consider developing an experiment using differential pricing to understand the price sensitivity of demand. These were beyond the scope of this study but we recommend that for any future studies on water demand. In particular, this shall be done during the detailed feasibility study of water supply sources. 


Reference 
ADB (2006), “Mid Term Report of Dhaka Water Supply Project - TA 4651 BAN” DWASA