COPENHAGEN, May 22 (Reuters) - Finnish plumbing and heating systems maker Uponor once more rejected a takeover offer from Belgian water management group Aliaxis , saying on Monday the bid had been "insufficient".

"The Board unanimously concludes Aliaxis’ current offer is insufficient in light of the company’s value and its future prospects", Hans Sohlström, head of the board committee, said in a statement.

The all-cash offer, which was announced earlier on Monday, valued the company at 1.87 billion euros ($2.06 billion) and represented a premium of about 54.7% to Uponor's closing price on April 13, Aliaxis said in a statement.

Aliaxis, which currently owns 20.16% of the company, announced on April 17 an intention to make a cash offer for Uponor. The offer was worth 1.82 billion euros, which the company rejected.

Oras Invest, Uponor's largest shareholder with about a 25.7% stake, said on April 17 it had no intention of accepting Aliaxis' unsolicited offer.

($1 = 0.9084 euros) (Reporting by Boleslaw Lasocki and Louise Breusch Rasmussen; Editing by Terje Solsvik, Jan Harvey and Chris Reese)