The reliability of a sprinkler system equals the reliability of its weakest link, the water supply. TS EN 12845+A2:2026 regulates water supplies along two axes: type (Clauses 9.1-9.5) and level of reliability (Clause 9.6). The two axes are independent of each other; the same type can be raised to a different level of reliability by a different arrangement. Source: TS EN 12845+A2:2026, Clauses 9.1 and 9.6, EN p.46 and p.55-57 (TSE p.49 and p.58-60).
1. Four types of supply (Clause 9.1)
Clause 9.1 (EN p.46) states: "Water supplies shall be one or more of the following:"
- a) town mains (in accordance with Clause 9.2);
- b) storage tanks (in accordance with Clause 9.3);
- c) inexhaustible sources (in accordance with Clause 9.4);
- d) pressure tanks (in accordance with Clause 9.5).
Clause 9.3.1 further divides storage tanks into three kinds: pump suction tank, gravity tank and reservoir.
2. Single water supplies (Clause 9.6.1)
Clause 9.6.1 (EN p.55-56) lists six arrangements as "acceptable single water supplies":
| # | Single supply | Constraint |
|---|---|---|
| a | Town main | - |
| b | Town main with one or more booster pumps | - |
| c | Pressure tank | LH and OH1 only |
| d | Gravity tank | - |
| e | Storage tank with one or more pumps | - |
| f | Inexhaustible source with one or more pumps | - |
Source: Clause 9.6.1, EN p.55-56 (TSE p.58-59).
The restriction of the pressure tank to LH and OH1 follows from the requirement that the tank must be able to meet the sprinkler demand until it is exhausted (Clause 9.5.4.1, EN p.54). Clause 9.5.3 (EN p.54) also gives the minimum water volumes: for a pressure tank used as a single supply, 15 m³ for LH and 23 m³ for OH1; for a duplicate supply, 15 m³ for all groups of LH and OH.
3. Superior single water supplies (Clause 9.6.2)
Clause 9.6.2 (EN p.56) defines the category as follows: "Superior single water supplies are single water supplies which provide a higher degree of reliability." There are three options.
a) A town main fed from two ends. All four conditions shall be satisfied:
- each end shall be capable of meeting the flow demands of the system;
- it shall be fed from two or more sources of water;
- it shall be independent at any point of any single common main;
- where only one end will give the required pressure, a single booster pump is installed. Where neither end will give the required pressure, two or more booster pumps are installed.
b) A gravity tank without booster pumps, or a storage tank with two or more pumps. The tank shall satisfy these four conditions:
- the tank shall be of full capacity;
- there shall be no ingress of light or foreign matter;
- suitable clean water shall be used (see Clause 8.1.2);
- the tank shall be painted or otherwise protected against corrosion; this protection shall be such that the need to empty the tank for maintenance is reduced to intervals of not less than 10 years.
c) An inexhaustible source with two or more pumps.
4. Duplicate water supplies (Clause 9.6.3)
Clause 9.6.3 (EN p.56):
Duplicate water supplies shall consist of two single water supplies, each of which is independent of the other. Each of the supplies forming part of the duplicate supply shall comply with the pressure and flow characteristics given in Clause 7.
Any combination of single supplies (including superior single supplies) may be used; there are only two constraints:
- a) not more than one pressure tank shall be used on OH systems;
- b) only one storage tank of the reduced capacity type (see Clause 9.3.4) may be used.
The pump side counterpart of a duplicate supply is in Clause 10.2 (EN p.57): where more than one pump is installed on a superior or duplicate water supply, not more than one may be electric motor driven. The suction side counterpart is in Clause 9.4.8 (EN p.54): "Separate suction and settling chambers shall be provided for duplicate supplies."
5. Combined water supplies (Clause 9.6.4)
A combined supply is a single supply feeding more than one fixed fire fighting system; the typical example is a combined hydrant, hose and sprinkler installation.
Clause 9.6.4 (EN p.56-57) first sets the level requirement:
Combined water supplies shall be superior single or duplicate water supplies designed to feed more than one fixed fire fighting system.
The NOTE carries an important warning: "Some countries may not permit sprinkler systems to be fed from a combined supply."
Then come the four conditions:
- a) the systems shall be fully calculated;
- b) the supply shall be capable of providing the sum of the simultaneous maximum calculated flows from each system. The flows shall be corrected by raising them to the pressure required by the most demanding system;
- c) the duration of the supply shall not be less than that required for the most demanding system;
- d) duplicate pipe connections shall be provided between the water supplies and the systems.
The link between a combined supply and pump separation
Clause 8.3 (EN p.43) is entitled "Connections for other services" and lists the four conditions for taking water from the sprinkler system for services other than sprinklers: the connections shall be as specified in Table 8; the connections shall be made upstream of the control valve set(s) through a stop valve fitted as close as practicable to the point of connection to the sprinkler system supply pipe; the sprinkler system shall not be a high rise system; and the sprinkler system shall not protect a multi storey building.
The final sentence of the clause regulates pump separation:
Sprinkler system pumps shall be separate from the pumps of any hydrant system, unless a combined water supply in accordance with 9.6.4 is used. Clause 8.3, EN p.43
The structure of the sentence is critical: the separation requirement is the rule, and a combined supply complying with 9.6.4 is the exception. Where a combined supply is used, the separation obligation falls away.
Table 8 (EN p.44) gives the connection sizes for other services:
| Type of water supply | Acceptable number, size and purpose of connections |
|---|---|
| Town main; main and supply pipe ≥ 100 mm | One, of not more than 25 mm diameter, for non industrial use |
| Town main; main and supply ≥ 150 mm | One, of not more than 40 mm diameter, for non industrial use; or one, of not more than 50 mm diameter, for fire hose reels, to which one further connection of not more than 40 mm may be made (for non industrial use), with a stop valve fitted close to the first connection and close to the supply end |
| Elevated private reservoir, gravity tank or automatic pump | One, of not more than 50 mm diameter, for fire hose reels |
NOTE: An additional supply arrangement with a check valve may be provided for the fire brigade.
6. Isolation of the supplies (Clause 9.7)
Clause 9.7 (EN p.57) requires the connections between the water supplies and the sprinkler control valve sets to be arranged so as to ensure three things:
- a) to facilitate servicing of the main components such as strainers, pump sets, check valves and water meters;
- b) that any problem occurring in one supply does not disturb the operation of another supply or source;
- c) that maintenance on one supply does not disturb the operation of another supply or source.
These three requirements are the pipework side counterpart of the "independence" in the definition of a duplicate supply.
7. The two places where a superior single supply is mandatory
The standard requires at least one superior single supply in two places:
| Place | Provision | Scope |
|---|---|---|
| Annex E.3.1 (EN p.140) | "The system shall have at least one superior single water supply." | Annex E applies to multi storey buildings where the height difference between the highest and lowest sprinkler exceeds 45 m (E.1). The requirements are directed at occupancies where the hazard is no greater than OH3; high rise systems with a hazard greater than OH3 require specific fire engineering solutions. |
| Annex F.6 (EN p.143) | "The system shall have at least one superior single water supply. NOTE: In some countries a duplicate supply is required." | Annex F applies, in accordance with F.1, where required by national regulations. |
The scope of Annex E is the height difference alone; it contains no special provision for HHS storage. The design criteria for HHS itself are in Clause 7.2, its water volume in Table 10 and its duration in Clause 8.1.1.
8. Summary of the selection
| Level of reliability | What it means | Clause |
|---|---|---|
| Single | One of six arrangements; pressure tank for LH/OH1 only | 9.6.1 |
| Superior single | Town main fed from two ends, gravity tank / storage tank with several pumps, or inexhaustible source with several pumps | 9.6.2 |
| Duplicate | Two single supplies, each independent and complying with Clause 7; only one pressure tank on OH, only one reduced capacity tank | 9.6.3 |
| Combined | A superior single or duplicate supply feeding more than one system; four conditions | 9.6.4 |
Frequently Asked Questions
How many types of water supply does EN 12845 recognise?
TS EN 12845+A2:2026 Clause 9.1 (EN p.46) lists four types: town mains in accordance with Clause 9.2, storage tanks in accordance with Clause 9.3, inexhaustible sources in accordance with Clause 9.4 and pressure tanks in accordance with Clause 9.5. The water supply shall be one or more of these.
What are the acceptable single water supplies?
Clause 9.6.1 (EN p.55-56) gives six options: a) a town main; b) a town main with one or more booster pumps; c) a pressure tank (LH and OH1 only); d) a gravity tank; e) a storage tank with one or more pumps; f) an inexhaustible source with one or more pumps.
What is the difference between a superior single supply and an ordinary single supply?
Clause 9.6.2 (EN p.56) defines superior single supplies as 'single water supplies that provide a higher degree of reliability' and lists three options: a town main fed from two ends (with four conditions), a gravity tank without booster pumps or a storage tank with two or more pumps (with four tank conditions), and an inexhaustible source with two or more pumps.
What constraints apply to a duplicate supply?
Clause 9.6.3 (EN p.56): duplicate supplies consist of two single water supplies each independent of the other, and each shall comply with the pressure and flow characteristics of Clause 7. Any combination of single supplies (including superior single supplies) may be used; there are two constraints: not more than one pressure tank shall be used on OH systems and only one storage tank of the reduced capacity type may be used.
With a combined water supply, must the sprinkler pumps be separate from the hydrant pumps?
The final sentence of Clause 8.3 (EN p.43) reads: 'Sprinkler system pumps shall be separate from the pumps of any hydrant system, unless a combined water supply in accordance with 9.6.4 is used.' In other words, where a combined supply complying with 9.6.4 is used, the separation requirement no longer applies.
Which four conditions must a combined supply satisfy?
Clause 9.6.4 (EN p.56-57): combined supplies shall be superior single or duplicate supplies and shall satisfy the following four conditions: a) the systems shall be fully calculated; b) the supply shall be capable of providing the sum of the simultaneous maximum calculated flows from each system, the flows being corrected by raising them to the pressure required by the most demanding system; c) the duration of the supply shall not be less than that required for the most demanding system; d) duplicate pipe connections shall be provided between the water supplies and the systems.
References
- TS EN 12845+A2:2026 Clause 8.1.1 Duration (EN p.42 / TSE p.45)
- TS EN 12845+A2:2026 Clause 8.3, Table 8 Connections for other services (EN p.43-44 / TSE p.46-47)
- TS EN 12845+A2:2026 Clause 9.1 General - the four types of supply (EN p.46 / TSE p.49)
- TS EN 12845+A2:2026 Clause 9.3.1 Storage tanks (EN p.46 / TSE p.49)
- TS EN 12845+A2:2026 Clause 9.4.8 Separate suction and settling chambers for duplicate supplies (EN p.54 / TSE p.57)
- TS EN 12845+A2:2026 Clause 9.5.3 Minimum water volume of a pressure tank (EN p.54 / TSE p.57)
- TS EN 12845+A2:2026 Clause 9.5.4.1 Air pressure and contents (EN p.54 / TSE p.57)
- TS EN 12845+A2:2026 Clause 9.6.1 Single water supplies (EN p.55-56 / TSE p.58-59)
- TS EN 12845+A2:2026 Clause 9.6.2 Superior single water supplies (EN p.56 / TSE p.59)
- TS EN 12845+A2:2026 Clause 9.6.3 Duplicate water supplies (EN p.56 / TSE p.59)
- TS EN 12845+A2:2026 Clause 9.6.4 Combined water supplies (EN p.56-57 / TSE p.59-60)
- TS EN 12845+A2:2026 Clause 9.7 Isolation of the water supply (EN p.57 / TSE p.60)
- TS EN 12845+A2:2026 Clause 10.2 Multiple pump set arrangement (EN p.57 / TSE p.60)
- TS EN 12845+A2:2026 Annex E.1 and E.3.1 High rise systems (EN p.139-140 / TSE p.142-143)
- TS EN 12845+A2:2026 Annex F.1 and F.6 (EN p.143 / TSE p.146)
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Download MEP Calc on the App StoreTS EN 12845+A2:2026 (EN 12845:2015+A2:2026) Fixed firefighting systems — Automatic sprinkler systems — Design, installation and maintenance; TS EN 12845-2:2025 (EN 12845-2:2024) ESFR and CMSA sprinkler systems. Every figure in this article is taken from the published standard text; clause, table and page references are listed under References. General information only, not a substitute for the standard or for a design review.