Rio de Janeiro has in recent years evicted drug dealers from hillside slums, carved fast-moving bus lanes into sclerotic streets, and cracked down on unauthorised food vendors along the city’s 93 km of beaches.

A projected six million people will attend this Carnival

Now, as they gear up for the 2013 Carnival, officials are taking aim at another old Rio scourge: public urinating.

Urine flows as freely during Rio’s famous annual festivities as beer and the cane liqueur known as cachaça.

For as long as locals remember, the sight of people relieving themselves – and the stench of their steamy puddles – has been as much a part of Carnival as half-naked women, samba schools, drag queens, body paint, and drunk and sun-burned foreigners.

But Rio, Brazil’s second-largest city and its most popular tourist destination, now wants to stop the peeing.

To sanitise some of the revelry, which officially started on Friday, the city hall has deployed thousands of agents to spot and detain offenders. It’s a dry run, if you will, before Rio hosts World Cup soccer matches next year and the 2016 Olympics – events that are also expected to inspire celebration. “It’s the biggest complaint we get,” says Alex Costa, Rio’s secretary for public order, echoing angry residents whose doors, curbs and car tyres get anointed by bursting bladders.

In recent weeks, the city has touted the number of mijões, or ‘pee-ers’, that agents have detained during pre-Carnival rehearsals and block parties: 321 since January 20, including 16 women and three foreigners.

Particularly lewd offenders are fined, but most detainees merely get shuttled to police stations where they miss the rest of the party.

“We just want to educate,” Costa says, “give people pause”.

The pee patrol is part of an overall effort to impose more order as Carnival’s popularity soars.

Not too long ago, a volatile economy and rampant crime relegated most of the celebration to a sterile, concrete promenade where professional parade organisers compete in a televised spectacle. It’s a far cry from grass-roots revelry.

As Brazil’s economy rebounded in recent years, city officials cleaned up Rio’s marquee neighbourhoods. Block parties and amateur street parades blossomed; adding to events expected this year to generate $665 million for the local economy.

In the past four years, the size of marches by neighbourhood groups, trade organisations, and other cliques has doubled, attracting a projected six million people this Carnival. Nearly 500 blocos, as the bibulous bunches are known, are scheduled to march by Carnival’s end on Wednesday.

To cope, the city has deployed 18,000 portable toilets around town. Along with thousands of police already on patrol, 7,700 municipal agents, more than twice as many as last year, control everything from unlicensed street vendors to illegal parking.

They’re also pursuing pee-ers.