What is water sharing

Bavarian State Office for
environment

General

At the end of the treatment and transport chain, which is characterized by extraction, processing and storage, there is water distribution in the water supply. It has the task of supplying the drinking water to the consumers in the entire supply area in such a way that it is available at all times in sufficient quantities, with sufficient pressure and in good quality.

Laying the drinking water pipeline

The water distribution as a public facility begins after the water treatment or, if no treatment takes place, after the water extraction and ends at the transfer point to the consumer (main shut-off device, usually the inlet valve in front of the domestic water meter).

The water is distributed through pipes in various materials and dimensions. The pipes themselves make up the main part of the pipelines; this also includes connecting pieces (depending on the pipe material), fittings for making branches, bends or transitions to other pipe materials, as well as numerous fittings (e.g. gate valves, vent valves, etc.) and finally devices for operating and maintaining the lines and, if necessary fire protection (underground and pillar hydrants).

A distinction is made between pipelines

  • Trunk lines
    are feeder lines over long distances
  • Feeder lines
    are water pipes between water extraction and supply areas.
  • Connecting lines
    are water pipes outside the supply areas that connect supply areas (places) with each other ..
  • Supply lines (local lines)
    are water pipes within the supply area in the built-up area.
  • Connection lines (house connections)
    are the water pipes from the branch point of the supply line to the transfer point (main shut-off device).

Pipe network shapes

When it comes to the hydraulic dimensioning and implementation of supply networks, a basic distinction is made between branching networks and ring networks (meshed networks), the latter being preferred due to greater security of supply. In the branching network, the individual supply lines branch off from the main or higher-level supply lines like branches of a tree and end as so-called stub lines. In the event of a supply interruption, all downstream power supplies are also affected. Due to stagnation problems, spur lines need to be flushed more frequently.

In the ring network, the individual supply lines are largely interconnected. The meshed networks guarantee a high level of operational safety, a more even supply pressure and thus a higher level of safety in the extinguishing water supply. In the event of a pipe rupture or other malfunctions, only a small section between two valves will fail, as the supply can be provided from two sides. The construction costs are higher than with the branching network due to the longer pipe lengths and a larger number of gate valves. In the established distribution networks, combinations of both network types predominate, whereby the respective advantages are used for individual network components.

Rating

The planning and dimensioning of a water distribution network has to be done in such a way that drinking water is available in sufficient quantity, good quality and with sufficient pressure at every point in the network.

When it comes to the hydraulic dimensioning of the pipelines, a basic distinction is made between three different so-called operating states that must be examined:

  • Operating state 1:
    Pump operation, largest promotion of a pumping station
  • Operating condition 2:
    highest hourly consumption in the distribution network on the day with the highest consumption
  • Operating condition 3:
    Extinguishing water withdrawal and highest hourly consumption on days with average consumption (places with more than 300 inhabitants) or without consumer consumption (places with less than 300 inhabitants).

The dimensioning of the individual pipelines is carried out for the greatest flow rate of the respective operating condition. The required minimum pressures according to DVGW worksheet W 400-1 for the respective operating condition must not be fallen below. The static pressure in the center of gravity of a pressure zone should be approx. 4 to 6 bar at the house connection. If an area has considerable differences in height, it is advisable to divide it into several supply zones with their own elevated tanks (or pressure reduction) and separate networks.

In municipalities with up to 10,000 inhabitants, pipes DN 80 - 250 are mainly used, whereas large long-distance water supply companies have pipe dimensions of up to DN 2500.

When determining the operating pressure of a pipeline, particular attention must be paid to pressure surges occurring in long-distance and feeder lines. Pressure surges are pressure fluctuations within the pipeline system that can arise from a sudden pump standstill and the rapid closing or opening of shut-off devices. If necessary, suitable technical measures (e.g. pressure equalization tank) must be provided that can safely absorb the pressure fluctuations that occur. The pipes themselves are manufactured with different permissible operating pressures (pressure levels) depending on the pipe material.

Fire water supply

According to the legislation applicable to fire protection, this is a task of the municipalities.

As a rule, the extinguishing water is provided via the public water supply system. If this is not (completely) possible due to hygienic or technical reasons, other options for extinguishing water supply (e.g. extinguishing water from streams, rivers, ponds or other extinguishing water tanks) must be considered.

In the case of smaller communities and districts in particular, the dimensioning of the pipeline network is mainly based on the aspect of the provision of fire water. On the other hand, in these cases there is a relatively low consumption by the customer, which leads to an increased dwell time and an associated risk of stagnation. In order to maintain the quality of the drinking water, it must therefore be considered in each individual case to what extent the provision of extinguishing water can be taken into account when dimensioning a pipe.

Further details can be found in DVGW worksheet W 405 "Provision of extinguishing water through the public water supply", including supplement 1 "Avoiding impairment of drinking water and the pipe network when extinguishing water is withdrawn" and DVGW Water Information No. 99 "Extinguishing water supply from hydrants in public Traffic areas ”.

Additional information

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