Where should I eat in Vienna, and which local food or drink is worth trying?

The first pipeline, the I. Wiener Hochquellenleitung, was opened by Emperor Franz Joseph I in 1873. It ran about 90 kilometers originally and runs roughly 150 today after further springs were connected, drawing on the Rax and Schneeberg area beginning at the Kaiserbrunn spring. The second, the II. Wiener Hochquellenleitung, was inaugurated at a ceremony in Vienna's City Hall on 2 December 1910 and covers about 180 kilometers from the Hochschwab massif in the Salzatal valley in Styria.

Between them, those two lines supply all of the city's drinking water in normal operation. Groundwater from the Lobau and Moosbrunn plants is added only during extreme heat or while a pipeline is being maintained. That is an unusual arrangement for a European capital of Vienna's size, and it is the reason ordering tap water here is not a compromise.

For produce, the name to look for in late spring is Marchfeldspargel — the asparagus grown on the Marchfeld plain immediately east of the city. It is a registered Protected Geographical Indication, entered under Commission Regulation (EC) No 1263/96 and amended by Regulation (EC) No 564/2002, with a further amendment approved on 13 February 2015 that named SGS Austria Controll-Co. GmbH as the inspection body. The designation is specific to the Marchfeld, not to Austrian asparagus in general.

The Marchfeld is flat, open farmland running east from Vienna's edge toward the Slovak border — the opposite landscape from the Alpine valleys the city's water comes from, and close enough that its spring crop reaches Vienna's markets the same week it is cut.

Marchfeldspargel is a place-bound name, which is the whole point of a geographical indication: asparagus grown elsewhere in Austria cannot be sold under it, however good it is. The registration dates back to 1996, so this is one of the older Austrian entries on the European register — long enough that the name carries weight locally rather than reading as a recent marketing exercise. If a menu names the Marchfeld, the sourcing claim is a legal one.

• Any season — Ask for tap water; it comes from the Rax-Schneeberg and Hochschwab springs rather than from treatment plants.
• Late spring — Marchfeldspargel is the protected local crop, grown on the plain between the city and the Slovak frontier.
• In high summer — This is when the city blends in Lobau and Moosbrunn groundwater, the only time its water is not purely Alpine spring supply.

Austria has a declaration threshold of €10,000 or the equivalent for currency, so a trip financed in cash needs that figure in mind. The State Department recommends six months of passport validity even though Austria's own minimum is three months beyond your planned departure from the Schengen area — plan to the longer number. And Marchfeldspargel is a seasonal crop with a short window, so a trip outside late spring will not find it, protected name or not.

The Vienna answer on timing explains the palace hours and the summer heat that puts the city's water system onto backup supply; the first-visit question covers the designated Historic Centre and ticket prices.