Offene Quelle – How to Conduct a Potential Analysis¶
Main question¶
Where can pop-up drinking fountains be mounted on hydrants, and how much would that improve access to drinking water in public spaces?
A hydrant is a technical candidate if it exists, can legally be used and delivers drinking-water quality. It is only a useful candidate if people need water there and no fountain is nearby. That's why the analysis has four modules: your three questions plus a demand and gap module.
All hydrants ──► legally and practically usable ──► drinking-water quality ──► where demand is high and supply is low
(M1) (M2) (M3) (M4)
Scope: start with one pilot city where you can get utility data, then scale up to similar cities (see M5). Analyse each hydrant individually.
M1 – Where are hydrants located?¶
Data sources
| Source | Content | Access |
|---|---|---|
OpenStreetMap (emergency=fire_hydrant) |
Location; often fire_hydrant:type=pillar/underground, couplings, fire_hydrant:diameter |
Open, through the Overpass API |
| Water utility GIS / hydrant plans | Complete stock, type, nominal size (DN), supply main, operating status | On request; usually needs a cooperation or NDA |
| Fire brigade hydrant registers | Location, usability | On request |
| Municipal open data portals | Some cities publish hydrant layers | Check per city |
Steps 1. Download OSM hydrants for the pilot city, for example:
[out:json][timeout:120];
area["name"="<City>"]["boundary"="administrative"]->.a;
node["emergency"="fire_hydrant"](area.a);
out body;
Output: a hydrant layer with type and position attributes, plus a statement on how complete the data is.
M2 – Which regulatory requirements apply?¶
This module produces two things: - Exclusion criteria that filter locations. Example: an underground hydrant in the carriageway is not usable. - Product requirements. Example: a backflow preventer is mandatory.
Areas to cover (check each against its current version):
| Area | Relevant rules (starting point) |
|---|---|
| Drinking-water hygiene | Trinkwasserverordnung (TrinkwV 2023): obligations for temporary water supply installations, notifying the local health authority (Gesundheitsamt), parameters to test |
| Backflow protection | DIN EN 1717, DIN 1988-100 |
| Hydrants and connections | DVGW W 331 (hydrants), DVGW W 408 (connecting outlets to hydrants), DIN EN 14384 / DIN EN 14339, DIN 14375 (standpipe) |
| Firefighting water | DVGW W 405: hydrant must stay accessible and usable at the required flow |
| Materials in contact with water | UBA assessment criteria for plastics, metals and other materials |
| Public space | Special-use permit under state road law (Sondernutzungserlaubnis), duty to keep the site safe (Verkehrssicherungspflicht), accessibility |
| Billing | Mess- und Eichgesetz: certified meter if water is billed |
| Policy driver | WHG §50 (since 2023): tap water in public places is part of public water supply |
Method: desk research, then expert interviews with a water utility, a fire brigade, a health authority and the road authority. Summarise the result in a requirements matrix: requirement → source → whether it filters locations or shapes the product → open questions.
M3 – Where do hydrants deliver drinking-water quality?¶
Hydrants on the public network carry drinking water in principle. At the tap, quality depends mainly on how long water has been standing and on the network layout.
First exclude hydrants that are not on the drinking-water network: firefighting-water wells, suction points, industrial water networks.
Desk indicators (from utility network data): - Supply main: looped vs. dead end, nominal size, material, age - Typical flow and water age in that part of the network (from the utility's hydraulic model, if one exists) - History: when the utility last flushed or serviced the hydrant, past turbidity complaints
Field campaign (together with the utility, sampled by an accredited lab): - Choose 10–20 hydrants that differ in their indicators. - Measure temperature, turbidity, and the TrinkwV microbiological parameters (E. coli, coliform bacteria, colony count) before and after defined flushing times. - Result: how much water must be flushed before the hydrant reliably meets drinking-water quality, and how that relates to the desk indicators.
Output: a quality class per hydrant (A: suitable after short flushing / B: suitable after longer flushing / C: unsuitable), derived from the desk indicators and calibrated with the field data.
M4 – Where is drinking water needed? (demand and gap)¶
| Factor | Data source |
|---|---|
| Existing drinking fountains | OSM amenity=drinking_water, utility lists, Refill stations |
| Heat stress | Municipal climate analysis maps, heat action plans, satellite land surface temperature |
| Footfall | Pedestrian zones, squares, parks, transit hubs, event sites (OSM, city) |
| Vulnerable groups | Population density and age structure (census grid), homeless shelters, care facilities |
Gap: the area or population that is not within a defined walking distance of an existing fountain (for example 300 m or 5 minutes, decided as a parameter).
M5 – Bringing it together¶
- Filter: M1 hydrants → apply the M2 exclusion criteria → keep only M3 quality classes A and B.
- Score: rate the remaining hydrants by demand (M4) and by how much of the gap they close.
- Outputs:
- Map of candidate locations, split into pop-up/event and permanent
- Key figures: number of suitable hydrants, extra population and area covered, share of heat hotspots covered
- Top-N locations for a pilot
- Scale up: apply the pilot-city factors (share of usable hydrants, quality classes) to similar city types to estimate a national potential.
Tools: QGIS; Python (geopandas, osmnx for walking-distance catchments, the Overpass API).
Open points and risks¶
- Access to utility data (network, hydrants, quality) decides how deep the analysis can go, so look for a cooperation partner early.
- How complete OSM hydrant data is in the pilot city.
- Flushing water use and its cost may limit locations in quality class B.
- The list of rules and standards in M2 still has to be checked against current versions and individual state law.